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LT250 LT500HQ > Performance Modfications > Jerry Hall wisdom

Title: Jerry Hall wisdom

Kyle T - April 6, 2013 02:11 AM (GMT)
These WILL be the 2 biggest and baddest posts you will ever read. It is all of the important Jerry Hall posts from another website. All are in order except the last 2. Every different post is separated by 5 spaces. Read and enjoy!

We have re-sleeved hundreds of LT-500 engine cases over the last 20 plus years. We have used steel, brass, aluminum and plastic for the case inserts. I will talk about why I prefer the plastic bearing inserts instead of the metal inserts when I have a lot more time to go into detail.


Why does the LT 500 Suzuki have problems with the bearing pockets wearing out? Our first guess was that the main bearing pockets were loose on the new engines. We started measuring the bearing pockets on new cases and found that Suzuki was setting the interference fit between the main bearing and the bearing pocket where it should have been. Our next observation was the problem seemed to appear on the “stockish” type engines that had a million miles on them or on the race engines. We began to see other problems, broken crank pins, and broken crankshafts on the ignition side at the junction of the main bearing shaft and crank web. We began to study the failures and the failures pointed to the cause of the problem. Before a part breaks, it has to flex. The flex leads to fatigue and the part will eventually crack and break in the fatigued area.

Crankshaft flexing is what wears out the bearing pockets. The majority of the flex occurs in the crank pin. Another area of flex is at the junction of the main bearing shaft and the crank web. How do we know that these areas flex? These are the two areas where the crankshaft breaks.

What causes flex? The two major factors that contribute to the flex of any crankshaft are high rpm and the load that the connecting rod exerts on the crank pin when the engine is under full power.

The connecting rod is experiencing high tension as the piston approaches top dead center, when the engine is at high rpm and the throttle is closed,. The piston is pulling on the connecting rod with a force of thousands of pounds. As the rpm is increased this force increases exponentially. This force causes the crank pin to flex so that the distance between the crank webs DECREASE in the area opposite the crank pin.

When the engine is under power, the piston exerts force on the connecting rod and the rod transmits this force to the crank pin. The peak pressure on the piston occurs in the neighborhood of 20 to 30 degrees after top dead center. When the power level of the engine is increased, the crank flexing force increases. The force on the crank pin when the engine is under power causes the crank pin to flex so that the distance between the crank webs INCREASE in the area opposite the crank pin.

The flex in the crank pin is not visible, but it exists on a micro level. For discussion purposes the main bearings should be thought of as being part of the crank webs. Looking at the motion of the crank webs described in the above paragraphs, we can easily observe the motion of the main bearings. The interference fit between the main bearings and the bearing pockets helps resists some of the motion of the bearings, but some movement of the bearing will occur when the crank pin flex exceeds a certain level.

The friction and extreme pressure between the outside of the main bearing and the bearing pocket causes micro welding to occur between the two surfaces when they are both iron based materials. The micro welding is what causes the pits to occur on these surfaces.

How can we prevent the problems described above?

One obvious solution would be to increase the diameter of the crank pin. Increasing the crank pin diameter would require an increase in the outside diameter of the crank webs if we are to maintain a reliable design. The proper interference fit between the crank pin and the crank web must be maintained in order to prevent movement between the web and the crank pin. I have never seen a stock LT500 crank web split between the crank pin hole and the outside diameter of the crank web. I have seen the crank webs split between the crank pin holes and the outside diameter of the crank web when the correct interference fit on the crank pin is used on stroker cranks. There is not adequate strength between the crank pin holes in the web without increasing the OD of the web. Welding the crank pins to the existing webs should not be considered as an option. Welding crank pins to the webs are just band-aids for a poor design or loose crank pin holes. A large diameter crank pin is also not desirable for high-rpm two strokes due to the increased moment of inertia of the bearing cage assembly and the pre-mix type of lubrication system

Another solution would be to run two main bearings on each end of the crank. This is not an affordable solution because it would require a new crankcase and crankshaft design.

We started seeing bearing pocket failures on the 1987 race engines before the 1988 models were released. The LT 500 engine was designed for power levels in the 40 hp to 50 hp range and engine speeds of around 6500 rpm. We often spin these engines over 8000 rpm and we can easily produce power levels in excess of 80 HP. The bearings are going to move in the bearing pockets when we elevate the power and rpm. So what is the best cost based solution?

We re-sleeved the early pocket failures with steel inserts on the first race engines. They did not seem to last much longer than a new set of cases that had cast iron inserts. The steel inserts would eventually get loose and had the pitting problem like the cast iron inserts. We used brass inserts and then silicon bronze. The bronze seemed to last longer but eventually wear out. The bronze did not show any pits when they got loose like the iron bases inserts. We also tried aluminum inserts and they eventually got loose without pitting. We eventually came to the conclusion that the main bearings are going to move in the bearing pocket. What can we use as material between the bearing and the cases that will minimize the wear? We tried using plastic for an insert material and watched these engines for a few years on different customer engines. Upon teardown the bearing pockets and the outside of the main bearings did not show any ware. We have used the plastic inserts in hundreds of main bearing pockets over the last 20 years in the LT500 engines.

I do not believe that there are any “cushioning” effects on the bearings as a result of the plastic inserts. I do not believe that there is any other magical properties of the plastic inserts other than it does not ware as fast as the metal inserts.


If there is oil in the fuel it will smoke. A two stroke gets its lubrication from the oil in the fuel. The oil that you put into the filler plug only lubricates the transmission.

On a premix type of lubrication system my experience has shown that one should mix the fuel / oil ratio for the worst-case situation. An engine that is ONLY going to idle will get all of the lubrication it needs at 80 to 100 to 1. A two-stroke that is at high rpm and has had its throttle wide open for more than about 5 seconds needs a 15 to 20 to 1 ratio. The oil injection systems on the snowmobiles and boat engines mix the oil with the fuel at the above ratios to suit the rpm and throttle position . After working on thousands of two strokes for over 35 years the oil ratio has proven to have a much larger role in engine reliability than the brand of oil in the general purpose two-strokes. In the most extreme cases like the 50 hp 125cc engines, the castor oil gives use the longest engine life. My testing has also shown that my two-stroke engines will make more power at 15:1 ratio than a 50:1 ratio if you have any tuning abilities.

It makes me happy when I see my customers engines smoke. It tells me that they are not going to have lubrication related failures. If you are having problems fouling spark plugs, you are using too much oil for the way you are riding your bike or you need to work on you carb tuning skills. One must mix the fuel, tune the carb and then ride it for the application for which it was tuned or suffer the consequences.

An engine use for recreational purposes usually needs more oil in the gas than a drag engine. It is not uncommon for recreational riders to spend 10 to 15 seconds or more running wide open down a dirt road or doing laps in a bowl at the sand dunes. The oil layer that is on all surfaces in the crankcase may not even reach the stabilization point when the throttle is closed on a drag engines extremely short periods of full throttle. The criterion that determines how much oil should be used in the fuel is the time spent at wide-open throttle! An 80 cc moto-cross engine will spend much more time a wide open throttle than a 250 on the same moto-cross track. … so the 80cc needs more oil in the fuel than a 250 for moto-cross application. Put a paddle tire on a 250 or run a 250 in a desert race and now the 250 requires as much oil in the fuel as the 80cc engine.

Why are you worried about white-ish smoke? It is a two stroke. It is suppose to smoke. Looking at the top of the piston and head does not tell you anything about your oil ratio. The top of the piston and head surface DOES NOT NEED LUBRICATION. Lubrication is only needed on frictional surfaces.

The top of the piston is clean because the piston has not experienced enough heat to char the fuel and oil that comes in contact with it. Cold piston crowns area the result of very brief periods of full throttle on a highly tuned engine or the tune of the engine is far from optimum. A two stroke that is properly tuned and ridden hard will not have a piston crown that looks new. The whole piston crown will be discolored and usually have a light layer of carbon on it.

We weld the ears first, then machine the base gasket surface of the cylinder next, then bore the cylinder. Sometimes we have to machine the reed gasket surface as well as the head gasket surface. The cylinder always needs to be bored after it is welded!

In the hundreds of cylinders that we have welded the ears on, I have never seen a welded cylinder that did not need at least .005" removed from the base to get it flat. You can bolt the cylinder to a big flat heat sink, weld the ears in small segments, and do all of the things that minimize warpage. It is going to warp.

We machine the base and head gasket surface on a special fixture on the lathe.


If the thrust washers on the crankshaft journal are large enough to center the rod between the crank-webs, you do not need the thrust washers on the wrist pin end of the rod.

We set the cylinder on a machined plate with a hole big enough that the sleeve can fit through the plate when doing a quick check with a feeler gage. You could also remove the base gasket and set it on your cases and use a feeler gage to check it for basic flatness. This method of checking assumes that your cases are flat. Most of the stock cases have about a .003" to .008" mismatch where the case halves meet under the reed valve portion of the cylinder. This is why the LT500s blow base gaskets in the back of the cylinder. We machine the base gasket surface on the cases on the majority of the 500s if we have to split the cases for transmission repair, bearing pockets or crank rebuilds. The bottom of the cylinder or the cases should have no more than .003" deviation. If your steel rule is straight, it looks like the ears are .020" to .030" low.

Divider plates in the carb bore, spiral bore carbs, knurled bore carbs, square bore carbs, upstream and down stream venturies in the carb bore, plastic inserts for under the slides, machining the pressure taps (bums) off of the bell mouths of the carb inlets, etc are modifications that are just SNAKE OIL. Some of the machine work on the bell mouth improves the air through the carb but destroys the slope of the fuel curve and makes the carb very sensitive and most often will not match the slope of the fuel curve that most engines require. I have tried and tested all of the modifications and concepts listed above. The carburetor manufactures around the world have also tested these concepts. Some of these concepts have been patented. Because something has a patent on it does not mean that it functions as advertised. The patent office just looks to see if any one else has registered the same idea. The idea could be beneficial and functional or just snake oil.

The carburetor manufactures would be incorporating these ideas into their carbs if they provided any benefit and would make their product superior. If the patented ideas had any benefit the carb manufactures would pay the royalties or buy the patent from the patent owners and obsolete their competing carburetor manufactures.

The majority of the enthusiast and a large number of the tuning shops do not have the test equipment, selection of jets, needles, slides, air correction jets or the experience to accurately test and evaluate these concepts, modifications or products. Most of the listed snake oils tend to improve throttle response by leaning the mixture in a particular throttle position. The same improvement in performance most often can be obtained through changing the appropriate metering device in your current carburetor.

Occasionally I encounter an engine that cannot be tuned because of something in the engine components are not working together. Using the wrong pipe with some porting combinations, using reed petals that have the tension adjusted incorrectly or the wrong petal thickness, and too much compression are the most common problems I find with un-tunable engines.

No. I do not see any purpose investing more time in a carb that is very deficient in its basic design. I did a lot of testing with the Lectron from about 1976 to 1979 or so when they were first released. I worked closely with Sparky Edmonds (the originator of the Lectron). He supplied me with every tuning part that was made. I was testing them on the factory moto-cross bikes and could not make them meter fuel at all throttle positions as well as the old round slide carbs that we were using at the time. I did a little more testing about 10 years ago. This Lectron carb had the power jet circuit. The original Lectrons did not have the power jet feature. Again, my testing indicated that the carburetor still needs more fuel circuits just like all of the other carburetor manufactures provide.

I think that the Lectrons design flaws are tolerable on a drag bike where metering fuel accurately over a wide range of throttle positions is not required. Putting a larger float bowl on them does not cure the fuel starvation problem (another design flaw), it just adds a little more time at wide open throttle to get you to the end of the drag strip before it runs the bowl dry. I will not waste my time trying to jet any carburetor that cannot supply enough fuel to the float bowl to maintain the same fuel level at all throttle positions and RPMs. Any time the fuel level changes in any float bowl type of carburetor, the air fuel ratio changes even though you did not change the jets.

The ratio I have found to work best in the majority of the engines is 100/0 water/water wetter. The only time I use water wetter is when you are racing on pavement and the sanctioning body will not allow any type anti-freeze or the glycol bases coolants. Using the recommended amount of water wetter will provide better corrosion control and water pump seal lubrication than using 100% water. I do not subscribe to their claims about water wetter significantly improving the cooling over a 50/50 mixture or water and anti-freeze.

I would not suggest using an override tranny for anything but drag racing. There are some guys that make what they call a dunable override, but these transmission require frequent shift fork replacement and have to be ridden in a certain way. When you do not ride in a certain way, many times gears start coming through the cases. On most override trannys you cannot let off the throttle without pulling in the clutch unless you are in top gear. I do not have time right now to explain how most overrides trannys work and limitations it places upon your riding style. I think that we need to educate some of the uninformed guys what they may getting into BEFORE they make the plunge.

It takes a little over a 100 hp on a Banshee to pull 70 mph on the steep part of the hill. Use the largest countershaft sprocket that will fit on the bike and get the ratio that works best for you by changing the sprocket on the axle. Small counter shaft sprockets consume more power than the large sprockets, small sprockets cause the chain to rub the swingarm and the tension on the chain is less with a large counter shaft sprocket.

The optimum shift point for each gear is determined by finding the part of the power curve that has highest average power between two RPM points. The two RPM points are determines by the transmission ratios theoretical RPM drop between shifts. I like to add about 10% to 15% more RPM to the theoretical RPM drop to allow for errors in shifting and the speed loss during shifting.

6 inches from the piston is somewhat of an industry standard for measuring EGTs on two strokes. Be careful when jetting the engine to produce the same EGT for each pipe. Different exhaust systems can produce different EGTs when they are jetted for maximum hp. I have seen 100 deg.F or more difference between pipes when they are tuned for max power. It typically takes 3 to 4 main jet sizes to cause a 100 deg.F change in EGT.

What EGTs will the tuners be looking for? Some engine pipe combinations will hole a piston at 1125 deg. F while other engine pipe combinations may live at 1300deg. F. I do not know what temperature the HPR19 pipe generally runs. I never used a temperature probe in the development of HPR19 in the field test or on the dyno.

My testing on two strokes has shown that the O2 sensor is not a useful tool for tuning a two stroke. The trapping efficiency and the O2 reading are directly related. When the trapping efficiency is high the O2 readings will tend to read richer than when the trapping efficiency is low. The trapping efficiency is highest at the torque peak. The O2 readings will indicate lean at the lower RPMs and in the over rev range because the trapping efficiency is poor. In general, a good pipe will give richer O2 readings than a poor pipe when the air fuel ratio in the combustion chamber is optimum.

My suggestion would be to just tune the carbs to find maximum power and watch the spark plug and the top of the piston for detonation. You may also find the temporary effects improper jetting will have on EGTs on the dyno. The temporary effect can "fool" the engine into "feeling" different pipe dimensions than what the engine will "feel" in the field when the dyno runs times are too short. Air flow over the exhaust is another key factor when dyno testing two-stroke exhaust systems.

If the test crew has any questions for me, let me know, other wise I will set on the sidelines and wait for the test results.

Remove the seal from the water pump impeller. Look at the area on the impeller where the impeller sets on the shaft. The shaft will imbed itself into the impeller. When this happens, the shaft will protrude above the surface where the rubber coated washer is suppose to seal. If the shaft protrudes above this surface, the rubber washer shoulders on the end of the waterpump shaft instead of sealing against the impeller surface. The water pump shaft cannot protrude through the impeller or it will usually leak. We have a modification for the impeller that eliminates the shaft imbedding itself into the impeller.

If all of the bolt holes and mounts do not align where you can start the bolts with your fingers and screw them all of the way in with your fingers, you WILL have problems with pipes and silencers breaking. It is imperative that none of the mounts are under ANY stress when mounting the pipe. Pipes have to fit properly to maximize their life span.

I have always found it to be just the opposite. 3.3 to 3.5 mm seats will usually hold a maximum pressure of about .5 to 0.7psi. Most carbs on a gravity feed system never see more than .4psi with a full tank of fuel.

The 1.5 and 2.0 seats will hold around 6psi.

The quality control on the OEM parts is much better than the Hot Rod Products. The price of the Hot rods also reflects the quality. We reject about 3 Hot Rod kits out of every 10 that are sent to us to rebuild cranks. They are much better than they were 5 years ago. Still, some are too tight, some are too loose, and some will have a taper on the bearing bore on the big end. You might be lucky to get a good one.

100LL av gas will work fine with most bean oils and most synthetics, if you will add a quart to 1/2 gallon of pump premium to 4 1/2 gallons of 100LL av gas. Most pump gas has enough blending agents that will help keep the bean oils dissolved in the av gas in the cooler temperatures. Shake the fuel can and immediately pour the mixture of oil and 100LL in to a clean jar or fill a jar from the petcock. If the fuel is cloudy the oil and fuel are not yet chemically compatible and need more blending agents added to the mix. Make sure the fuel/oil mix is crystal clear and never attempt to tune an engine running cloudy fuel.

I do not like the Keihin because you cannot replace the needle jet or the float valve seat when they become worn. Keihin carbs have to be replaced when these circuits give problems. The Keihin carbs have two less tuning circuits than a Mikuni.

Sticking floats are easily repaired on a Mikuni.

The number of tuning circuits in a carb is directly related to how precise the fuel metering can be tuned for a particular application. The Mikuni and Dellorto carbs require more experience and a much better understanding of fuel systems than a Keihin or Lectron carb.

I classify a carb size by measurement at the MINIMUM bore through the carb. Some measure the maximum bore any where they can find it. I do not like to bore a TM 38 larger than 41.5mm. When a TM38 carb gets a little ware on the slide or slide bore, we often encounter inconsistent idle speed when going larger than 41.5mm. Some carbs that have a taper bore may be classified by some as a 42.5 to 47mm. Lectron plays the "use the largest diameter they can find" measurement game. Some of their 48s are around 43mm to 44mm at the minimum bore.

It is the turbo that is making the power not the E85. Would this same engine run on premium without detonation? If not, the octane rating of the E85 may be just high enough to keep that particular engine out of detonation trouble. The engines I have tested behave like the octane rating is not as high as the E85 industry is promoting. The engines I have tested behave like the octane is somewhere in the 95 to 100 octane on the motored scale. There are two methods for testing automotive fuels. One is the research method and the other is the motored method. The octane rating of pump gas is an average of the two methods. Most race fuels use the motored method to rate the octane of their fuel. An engine will many times detonate it self to death on fuel that has a research number of 105 to 110 where the same engine run on gasoline rated at 100 octane on the motored method will run without detonation.

Flex fuel engines have more problems with cylinder rust when the engines are not run frequently than a gasoline engine that is not run for the same period of time. 15% gasoline in E85 just slows down the corrosion process and makes the engine start a little easier in cooler climates. The fuel-injected engines do not have the same corrosion problems with their fuel systems that carburetors experience that use ethanol or methanol. You have to have oxygen present before oxidation (rust or corrosion) can occur. Any of the fuels in the alcohol family will have corrosion problems when left setting in a carb. There is sufficient oxygen present in the float bowl to promote corrosion.

The discoloration, on the underside of the piston crown has very little to do with the cooling system unless your average coolant temperatures is over 200 deg. F. Color on the underside of the piston is only an indicator of piston crown temperature. The Wiseco piston was not designed for long periods of running at high loads. A drag motor that is properly jetted, has a properly machined head and has short run times of about 5 seconds will not usually have much discoloration on the underside of the piston. A good engine design with the proper exhaust system that is jetted rich enough to have a slight rich misfire at wide open throttle and is used for hard dunning, flat track or desert racing will often have ash on the underside of the piston. A well tuned engine that is operated for periods of wide open throttle of 20 seconds or more will often have ash on the underside of the piston.

An exhaust system that has too much restriction for the power being produced will also cause unnecessary piston crown overheating.

What do you do if you have ash on the underside of the piston?

1. Make sure you power valve is adjusted properly. A LT 500 that is run with the power valve open at the higher RPMs can overheat pistons!!!!!!!!!!
2. Make sure that your squish clearance is less than .055”.
3. Do not operate the engine at less than ½ throttle at high RPMs for more than a couple of seconds at any one time.
4. Use an exhaust system that has the correct restriction for the power being developed.
5. Use fuel that has an octane rating that is over what your engine design and operating temperature require.
6. Use a carburetor that meters accurately at ALL of the throttle positions that your riding style uses.
7. Reduce your compression ratio.
8. Use an ignition timing setting that is correct for your engine design and riding style.
9. Reduce your average coolant temperature.
10. Reduce the time the engine is operated at or near full throttle at any one time

We develop engines and pipes bases upon what our customer’s are using their engines for. Our most popular HPR 19 pipe for the LT 500 was developed for one of our drag engine packages. We tested the HPR 19 on milder porting packages and compared it to some of our old medium volume pipes that we developed in 1987 and 1988 The HPR 19 system made more usable power than our old 1988 HPR 3 pipe. The HPR 3 pipe had more usable power than the other pipes from that era. The HPR 3 pipe was snaked around and fit into the same area of the bike like the FMF, Bills, Paul Turner ..............etc....pipes. The HPR3 pipe had more volume than all of the pipes from that era. The HPR 3 pipe had the largest diameter mid section that we could fit into the space available. We stopped developing any larger volume pipes because customers were not ready to cut their plastic, make the pipe a leg burner by routing the pipe on the left side of the bike and could no longer wear shorts when they rode. 20 years later the mindset of the market began to change, so we continued development in 2005 on larger volume pipes.

We did some serious development on the 1985 and 1986 LT 250 engine package. Greg Clark won the National Mickey Thompson Championships on our 1985-1986 engines and pipes. We continued our development on the 1987 LT 250 but the technology Suzuki incorporated into their 1987 and later cylinders was inferior to the technology Honda incorporated into their 1987 and later 250Rs. We could not find the power to be competitive with the new Hondas and we did not have a Gary Denton riding for us, so we started developing the 250R Hondas.

I am not down on the LT250s. There are considerable power gains that can be made on any of the LT250s, but at a national level of competition they come up a little short even when money and time for development is not an issue for some customers.

I have tons of porting and pipe designs in the filing cabinets that we generated when we did all of the LT 250 development. I just do not know if the pipes that we built back in the late 1980s are any better than the pipes that are currently considered to be state of the art for the LT 250s.

The majority of the high profile, high volume pipe manufactures do not do cutting edge development on the new engines right after a new model is released. They typically wait 6 months or more to see what designs look like that the winners at the national level are using. After this time period they begin advertising their new pipe. If the advertising generates sufficient interest, they will start building their stamping dies and begin production.

I have NEVER had to give this speech after tearing down a customer's engine:

"Sir, the reason your engine failed is because you are using too much oil in your fuel"

I have given this speech probably a thousand times to customers over the years:

"Sir, the reason your engine failed is because you are not using enough oil in your fuel for the way you are operating engine".

The throttle position, RPM and the time the throttle is at wide-open throttle determines how much oil needs to be in the fuel. An engine needs about a 20:1 ratio any time the throttle is wide open for more than about 5 seconds. An 80:1 to 100:1 is all the engine needs when it is idling. We run some of the Kart engines that run on tracks with long straight a ways at about 15:1.

You cannot judge how much oil to run in the fuel by observing how much smoke comes out the pipe. A two stroke is supposed to smoke. If it does not smoke it is probably not getting proper lubrication.

Do not fall for some of the common advertising statements and myths that will eventually cost you some of your hard earned cash:

1. This oil is refined/blended from the best and most expensive base stocks, .................therefore it does not require you to use as much oil in the fuel.
2. A two-stroke engine will make more power if you put less oil in the fuel.
3. Running more oil in the fuel creates higher engine and exhaust temperatures.
4. Running more oil in the fuel requires you to richen your jets many sizes.
5. Running more oil in the fuel will carbon up the power valves much quicker.

Two-stroke oils cannot be tested using the standard testing procedures and equipment that are used to test conventional motor and transmission oils. Be cautious of the oils and their recommended ratios from companies that used these testing procedures when comparing their oils to other two stroke oils.

To summarize two stroke oils and ratios from 35 plus years of working on two stroke racing engines:

"The quantity of oil you put in the fuel is much more important than the brand of two stroke oil you use or how much the oil cost".

Yes that is usually true and a 20:1 ratio will usually make more power than a 32:1 ratio at wide open throttle.

That is because he has run similar test.

Any one that does any type of testing and knows how to interpret the results will come up with the same answer.

Science is wonderful. Without it, our world would not function. The laws of nature (physics and chemistry) always repeat. When scientific principles and procedures are repeated, you will always get the same results. If a scientific process did not repeat, an airplane would fly one time and the next time it would not fly. If a scientific process did not repeat, the next time you start your quad, popcorn could come out of the exhaust pipe instead of exhaust. If a scientific process did not repeat, the next time we port a cylinder or build and exhaust system we would get different results.

Building an engine is just like cooking. If you use the same blueprint and build the engine exactly to the print, you will have another engine that produces exactly the same power. If you follow every detail in recipe to bake a cake, you will get exactly the same cake every time you use that recipe.

Like Iceracer said, the head gasket problem is a simple problem to repair.

The only similarities between the KX500 and the LT 500 are the bore and stroke are the same. The later model KX 500s have multiple exhaust ports, it has real power valves, the power valves are actuated by a fly ball mechanism, it has a flat top piston, it has a larger diameter wrist pin and has superior heat dissipation because of the plated bore. The technologies of the two engines are light years apart.

This is just another example and side effect of using the thin walled re-sleeve jobs. The cylinder pictured has had a thin-walled sleeve installed inside the existing iron sleeve. The outer part of the original sleeve has broken away. The heat dissipation of an iron sleeve in an iron sleeve is very poor.

The entire original iron sleeve has to be totally removed when a thick walled sleeve is to be installed. A good sleeve is about 1/4" thick down in the area where the ports are located. It takes a lot more machine time when installing a thick sleeve. The cost of re-sleeving a cylinder with a heavy sleeve and labor is usually $100.00 to $150.00 more than the one in the picture. Unfortunately, we see these types of problem on a daily basis on work that was sold on Ebay and in the magazine adds. Be careful when considering who you send work to. There is an obvious reason that they have to advertise. Repeat business and word of mouth keeps the good shops swamped with work.

You are blowing head gaskets because the inner liner has dropped and the outer sleeve sealing surface is missing. The discoloration on the inner sleeve indicates the inner sleeve has not been making contact with the gasket. The outer sleeve has been the surface that has been providing the clamping force on the gasket except where the piece of the outer sleeve is missing. From the looks of the picture, I would not be surprised if the inner sleeve has dropped at least .002” below the outer sleeve.

I would remove the studs and have a qualified machine shop remove just enough material to make the two sleeves even with each other. Install a new gasket and give it a try. If it blows another gasket you should put a good thick-walled sleeve in the cylinder and eliminate your problem.

The air filter needs about a 4inch opening not a 2 3/4 inch opening when using an extension between the carb and air filter.

Titanium is a material that is stronger than steel for a given weight. Titanium is a poor choice of material for a counter shaft sprocket. Carburized steel would be the best choice of material for a countershaft sprocket. Titanium would be better than aluminum for the sprocket on the axle and it will resist abrasion better than aluminum, but not any where close to carburized steel.

Check the new sleeve and determine if it has dropped below the aluminum head gasket surface. The sleeve only as to drop 0.002 inches for the head gasket to start leaking. This is a common problem for shops that do not know how to properly install a sleeve.

Yes, the aluminum sleeve COULD conduct heat from the bore better than the iron sleeve but the amount of heat that makes its way to the water jacket is about the same. The real problem with ANY sleeve of ANY material is the poor heat transfer through the junction of the sleeve and the cylinder casting.

Heat moves through metal through a process called conduction. The conductivity of aluminum is almost twice as high as iron. Any time heat has to move through a gap or crack, the heat moves across the microscopic gap through a process known as convection or radiation. The convective heat transfer across a gap is about the same for all metals.

The advantage of plated bores on OEM cylinders is; the plating is applied to the surface of the bore of the casting. The electro plating process joins the molecules of the plating to the aluminum. The heat transfer is not hindered as it flows from the plating to the metal it is bonded to. The heat moves from the plating to the aluminum casting and through the casting to the water jacket as it was one continuous piece of metal without any discontinuities. Even though the junction of any sleeve and cylinder has a smooth surface and is a press-fit, the heat transfer across this junction is very poor as compared to an OEM plated cylinder.

A solid cast iron cylinder will conduct more heat from the surface of the bore to the water jacket than an aluminum cylinder casting with an iron or aluminum sleeve. The absence of the sleeve junction in the solid cast iron cylinder is why it will conduct the heat much better. The problem with a solid cast iron cylinder is it would weigh a lot.

I share the same strengths issues with WestTex on the aluminum sleeve. The LT 250/500 iron sleeve is very thin and fragile in the intake area and the portion that protrudes below the base gasket surface. The aluminum will be more fragile than iron because the aluminum is not as strong as steel for the same thickness. The portion of the sleeve that protrudes below the base gasket surface on plated OEM cylinders is usually at least 5/16 inch thick or thicker.

The engine could care less what gear you are using. The engine produces the same shape power curve in all gears. The amount of power that gets to the wheels does vary because of the parasitic losses produced by the transmission. The parasitic losses are highest in 1st gear and decrease with each successive shift. 4th and 5 gears on the LT500 will usually show the highest power delivered to the rear wheels.

The engine RPM drop is also different each time you shift. The RPM drop is the greatest when shifting from 1st to 2nd gear and about the same from 4th to 5th depending which gear box you have. The RPM drop between 2nd and 3rd gear is the same for both the 87 and 88 and later gear boxes. The RPM drop between gears is what I look at when designing porting and pipe combinations.

Any well-developed engine combination HAS TO HAVE sufficient power to produce acceleration at the RPM the engine drops to when a shift is made. If this does not happen you need an engine build that has all of the right components that compliment each other. A drag engine that does not pull hard every time a shift is made in all of the gears used will not be a good drag engine. The power band is too narrow for the transmission.

Recreational engine packages need to have a wider power band than a drag engine. A wide power band is another way of saying the engine has sufficient power at the RPM the engine will pickup the next gear if short shifted and still produce good acceleration.

I think I know the point you are trying to make and I generally agree with the point. The engine that makes a little less peak power but has a wider and flatter power curve will usually win most drag races. I can think of some power curve shapes where the engine that has 5 more hp would win a drag race and I can think of a few power curve shapes that have 5ft-lbs more torque that could also win the drag race. Show me the two power and torque curves and I can answer the question more accurately. It really depends upon the RPM where peak torque occurs and what the torque curve looks like after the torque peak.

The widths of the chain doesn't have much to do with the strength of the chain. The strength of the side plates and the strength of the pins are what really determine the strength. The diameter of the pins, the thickness and shape of the side plates is what I usually look at first then the material and heat-treat of the plates and pins if given. The chain manufactures will not usually give you the technical metallurgical properties of the chain. The tensile strength is most often a good summary of all dimensions and properties combined.

The following is an answer I gave to this question on another forum last week when asked What do you think about piston boost ports?

Every two-stroke responds differently. Some engines with boost ported pistons show a power gain, some show a power loss and some show no change in power.

Boost ports in the pistons can improve the flow INTO the crankcase during the intake cycle on some engines. Boost ports on some engines can improve the flow to the rear transfer port during the scavenging phase. Boost ports can allow the exhaust system to communicate with the intake system during the later stages of the scavenging cycle. Boost ported piston can sometimes reduce piston crown temperatures. There is not a yes or no answer favoring boost ports when applied to all two-strokes.

Engine development is a time consuming and expensive process. We do not have the time to consider every possible modification or design on every engine test during engine development. Predicting how a two stroke will react to a particular modification is more complicated than trying to predict how a woman will react to a comment or situation. You just have to try it and see what happens. Sometimes the result is rewarding and sometimes you wish that you had never opened that can of worms. Every engine and every women may react differently to the same situation. We have to learn from our mistakes (experience). The boost port question has to be answered on each model of engine and many times on each port and pipe combination.

The boost port question as applied to the LT500 Suzuki:

I have tested a lot of different modifications on the intake skirt and transfer openings on the LT 500. When I add a boost port to the pistons, which have my intake skirt and transfer opening modification, my dyno test show there is no power lost or gained. The boost port modification only weakens the piston and cracks will start originating from the boost port. On my LT500 pistons I do not use the boost port.

Do not power coat anything aluminum. The temper of aluminum changes any time 300 deg. F is exceeded. Like someone previously stated, The powdercoat is cured at over 400 deg F. The aluminum gets soft and looses it's temper.

You HAVE to eliminate the overflowing float bowl problem first. A carb cannot be tuned with the float level incorrect or fuel overflowing.

Replace the needle jet. They become worn and flow more fuel than what the numbers indicate. I have a bore gage that I can measure the inside of the needle jet hole. It is not uncommon to find the hole worn as much as .0015". A needle jet with that much ware will make the mixture very rich at an idle up to about 1/2 throttle opening. If you are duning this 500 I would use a R-4 or R-6 to help reduce partial throttle detonation.

If you are riding with the kids on smaller bikes or do a lot of low speed riding you will probably need an R-0.

DO NOT worry about oil dripping out of the silencer or the exhaust flange. Two strokes are suppose to burn oil. DO NOT reduce your oil ratio try to reduce the mess. Oil dripping out of the silencer is an indication that you are not doing much full throttle operation. A two stroke running a 10 to 1 oil to gas ratio will be dry and almost soot free at the end of the silencer if you are running the engine at full throttle. There is not enough heat in the pipe to burn all of the oil when you ride them easy.

Carb specs:

ONLY USE GENUINE MIKUNI JETS!!!!!!!!!!!!!!!!!!!!!!!!

Lid on the air box, foam filter 350 to 390 main jet
Lid off of the air box foam filter 380 to 470
Pilot jet 22.5 to 25
Needle 6DK3 2nd or 3rd clip position from top
Needle Jet R-0 to R-6 389 series
Air screw 1 1/2 turns out from the seated position Plus or minus 1/4 turn
No air correction jet
4.0 slide
3.5 needle seat
float arm parallel with the gasket surface (without the floats touching the float arm)

If your bike does not run good and reliable with the above jetting range YOU HAVE OTHER PROBLEMS WITH YOUR ENGINE OR ELECTRICAL

We still rebuild and do engine modifications (head mods and porting and an occasional custom pipe) to the specifications that resulted from my testing I did over 20 years ago on the LT 250s. I just do not know how the engines built to those old specs would perform when compared to the engines that have been built by the engine builders that claim to have done more recent testing (or are they also using old technology today). If a group of LT 250 owners would finance a development project, I could probably find some power that has not been found in these old engines. It just requires wearing out a bunch of engines on the dyno and doing a lot of field-testing to see what level these old engines could actually be taken to. It takes a lot of time, some engine parts and building many test pipes to develop and engine into a real power king.

The preliminary testing and development that I did back then indicated that the LT250 was lacking some basic engine technology and probably could not be developed to equal or surpass the power curve shape and power levels that the Honda 250s were capable of producing. Remember we had to build 250s not 270s, 300s, etc out of the LT 250s and the TRX 250s. We were building engines for the national racers. Big bores and stroker engines were not legal at that level of competition.

You never know exactly what you are getting when you buy a used lower end. You could be at the same place you now with a used lower end in a short period of time. If you go through your lower end and do it right, you should expect the rebuilt lower end to have about the same life span as a new lower end.

If the bore is straight and round you may be able to put in a new 89.5mm piston back in it. The pistons usually wear faster than the bore. If you keep the dirt out of the motor and run a lot of oil in the gas, it is not uncommon to be able to put 2 or 3 new pistons in the same bore!

If you decide to use a piece of hose on the HPR 19 pipes, continue to use the heavy spring that holds the pipe stinger and silencer together at their junction. The spring is essential to balance the loads on the pipe and silencer mounts.

If there is not more than .001" to .002" ware in the cylinder I usually do not recommend honing the cylinder. Honing ALWAYS increases the bore diameter and the piston to cylinder wall clearance. The compression ring does not really need the rough honed bore surface to promote quick ring break-in. The cylinder pressure exerts a tremendous inner force on the compression ring and pushes the ring against the bore. A freshly honed cylinder will make the compression rings seat about 5 to 10 minutes sooner than ring replacement without honing. A freshly honed cylinder is a little more abrasive than a bore that has some time on it and will increase the initial ware rate on the piston.

If the bore diameter is 88.20mm there will be about .011” to .012” piston to cylinder wall clearance. This is too much clearance. The rings will be ok at this size but the piston will soon develop cracks with this much clearance. We usually set the clearance on the LT500s with a Wiseco piston at .0045” if the customer is going to break-in the engine properly. If the engine is going to be used for drag racing only and the passes are going to be made on a COLD cylinder, we set those cylinder clearances to about .0055 to .0060”.

Worn rings in a two stroke rings have nothing to do with “blowing oil”. Due to the design of the two stroke engine, oil is in the fuel and the oil is burned when the fuel burns.

The 2nd ring in a four stroke is an oil ring. The oil ring in a four stroke will seat much quicker with a freshly honed bore on a four stroke racing engine. The oil ring may take 10 thousand miles or more to seat in a passenger car if the cylinder is not honed when installing new rings.

Measuring the end gap of used two stroke rings is not a good method to use when evaluating the ring condition. Using the light check method will reveal rings that need to be replaced long before the end gap will increase a few thousands. Wipe the bore and rings to remove all oil and dust. Place the ring in the cylinder and use the piston to “square up” and push the ring about half way between the top of the exhaust port and the top of the cylinder. Place a bright light in front of you with darkness behind you. Strategically hold the cylinder so that one can sight along the bore and look for daylight passing between the ring and the bore. The ring will ware where the bridges are between the ports, near the end gaps and where it passes over the exhaust port. If light passes between the ring and bore in any of these areas, replace the ring even if the end gap is still in spec.

28 ft. lb on a 8mm stud will pull the threads on the cylinder. 28 ft lbs on the 10mm studs will distort the bore. Just o-ring the head and rid yourself of the night mare and expense of conventional head gaskets. An o-ring head will seal when the nuts are just tight enough that they will not vibrate off. I usually torque the o-ring heads to 18 ft lbs regardless of the stud diameter.

The pipe will get about 1100 at the cylinder, 500 at the center section and 900 deg F at the stinger.

Do not use the 6 series needles in the VM 40 through VM44s where the 7series needles are used. The 6 series needles are too short and could pop out of the needle jet and cause the throttle to stick in the wide open position. The 6 series have a smaller initial diameter which will result in an extremely rich condition at initial throttle opening.

hope that the Sabertooth runs better than the 431 Puma. A customer just put a 431 Puma together and brought it to me to dyno to see how much power the kit made out of the box. It made 46 to the rear wheel out of the box. After 3 hrs of swapping pipes and optimizing the jetting, it made 49 to the rear wheels. That is pretty sad after spending over $2500.00 on the Puma cylinder kit, stroker crank and other necessary items and it would not make as much torque and HP as good as a well developed TRX 250R.

My 250 TRXs that I use to build for the national racers will make over 50 HP to the rear wheel on my dyno. The 250s will make more power and torque from 6100 to 9000 RPM than this big Puma. The 250s that we ran on the national circuit could not have the displacement any larger than 254.0 cc

Any thing can be made to FLY when we have enough spare parts to ware out on the dyno. It is ok if someone wants to spend the money to develop an engine of that size to produce 80 to 100 hp for drag racing. That is what we do for a living. Customers should not have to pay me to do basic engine design that should have been done by the manufacturer of the kit.

My point was: the manufacturer should have done their home work so that the kit will make at least 60 to 70hp out of the box. I do not think a company should pour some molten aluminum into a mold and then let the public finish the cylinder and pipe development at the public's expense.

Most customers expect an engine that is sold as a state of the art high performance kit with over 400cc of displacement to make at least as much power as a decent running 20 year old 250 Honda. Why should someone spend over $2000.00 for a big bore kit to go slower than their old 250

I have not found ANY two stroke oil that I would run at 50 to 1 in a motor that is run hard. The oil that has the most influence of engine longevity is the air filter oil, then comes the oil ratio and then the brand of two stroke oil. If all your engine does is idle, 80 to 100 to 1 will lubricate it just fine. If the engine only runs under full throttle 15 to 20 to 1 may be necessary.

The only significant break through in two stroke oil technology that I have seen in the last 20 years or so, is the amount of money being spent trying to convince the buyer that one brand of oil is superior to another.

It would take a inline cooler 10 feet long to reduce the temperature 2 to 3 deg C. All of the inline coolers I have seen are just bling and added restriction to the coolant line.

I do not believe there were any 87 to 92 LT 250s built by anyone that would ever show 50+ HP to the rear wheels on my dyno. There may be some big-bores on alcohol or on the bottle than make 50 + HP, but not an engine on gas and less than 260cc.

The type of ignition coil does not have any influence on the spark plug heat range that an engine needs. The optimum spark heat range depends upon the combustion temperature, the rpm of the engine, and the temperature of the head where the spark plug threads are located.

88 and later have the large hub. If the rivets are loose the hub has lost its ability to be perfectly centered. It is best to weld them before the rivets get loose. If the rivets are loose or some of the rivets have broken, damage to the stator coils will usually result.

I make 3 welds about 3/4" long with my tig welder. If you make the welds look the same you should not need to have it balanced.

It will slightly stronger if is not welded 360. Just make 3 equally spaced welds about one inch long.

300 to 500 ft. drag engine can run less oil in the fuel than a play bike than is being run hard!!!!!!!! An engine should have more oil AND more fuel (bigger jets, richer needle setting) for break-in. I recommend B8ES or equivalent for anything other than alcohol.

It is impossible to give an accurate starting point for jetting a bored out TM38 Mikuni without knowing more information about your engine package, type of silencer and air filter setup.

I read through the spark plug reading thread on this site a few weeks ago. Some of the statements in that thread trouble me and will cause some of the less experienced guys to possibly hurt their engine. I will try to make some additions to that thread when I have more time. In the mean time, tune your carb so that you can hear that it rich and do not worry what the spark plug looks like.

I do not window my LT500 pistons. All of the dyno testing on the LT 500 I have done, shows the window does not help or hurt the power. I cut my pistons differently than the other engine builders modified pistons that I have seen. Any machine work on the piston ALWAYS shortens the life of the piston. Some modifications shorten the life more than others. There is ALWAYS a decrease in piston life when engine power goes up. You have to build an engine whose power level and piston life fits your budget.

What year carb do you have?

What state of ware is the slide and slide bore in?

What condition is the choke circuit in?

Does the choke plunger seat properly?

Are you using genuine Mikuni jets?

Is the needle jet new or used?

Needle jets ware out and will make the engine very rich at or near closed throttle.

Does the engine have any air leaks?

Are your main bearings and main bearings tight? If these are loose the engine may leak check ok with the engine off but leak when running.

What condition are your reeds in?

We cannot help you until all of these questions are answered.

You may have other problems and trying to fix another problem with jetting.


The poor quality control on the thrust washers has allowed the hole for the wrist pin to be sloppy and the inconsistent heat-treating are the primary reasons that the steel washers fracture. The above text on stress risers is correct but the steel washers "rattling" on the wrist pin kills them quickly at high RPM. The thrust washers experiences tremendous acceleration and deceleration loads 4 times every engine revolution. When the thrust washer "rattles" on the wrist pin this makes the acceleration and deceleration loads even higher.

It is not good engineering practice to allow similar metals to “rub” together under high load. This is why we do not use a cast iron piston ring on an iron sleeve. A chrome ring on a cast iron bore will last a long time. A cast iron ring running inside a cast iron bore will ware both the ring and bore very rapidly. The steel thrust washer running on a steel wrist pin wares the wrist pin and thrust washer very rapidly.

Be careful putting the Paul turner silencer on a built motor. The inside diameter of the stinger tube and silencer is too small. It is just small enough that it doesn't effect the power but will lead to piston crown overheating and engine destroying detonation.

As stated in another post, oversized head gaskets and oversize pistons for future rebuilds seem to dry up in many cases. Most of the big bore kits move the bore too close to the head studs. This causes two problems.

There is a lot more distortion to the bore next to every head stud. The removal of material to accommodate the larger sleeve also allows the cylinder to distort more when the cylinder fires. The golden or brown streaks on the bore between the studs are the result of this for mentioned cylinder distortion. These streaks are areas where the rings are not making contact with the bore.

The increased flexibility of the cylinder and insufficient clamping surface between the bore and studs leads to common head gasket problems associated with big bore kits.


You cannot get more low end by keeping the valve open longer.

Closing the valve too late will cause power to dip at the higher RPM and can lead to destructive detonation.

There is one correct spring tension setting for your porting and pipe combination that will give you the best overall power everywhere if the system consistently repeats the engagement RPM.

Look at Rogue1970's dyno charts.

Less than .002 inches up and down and .005" to .008" endplay is normal internal clearance in the main bearings. More than .015" endplay is usually an indication that the right hand side bearing is loose in the case.

More than .003" up and down is an indication of one or a combination of problems exists. The main bearing needs to be replaced, the bearing pockets are worn out, and or the left end of the crank has ware were the bearing presses on to the left side of the crankshaft.

Use the 1.25 pitch. 1.50 pitch is the wrong design for head bolt application.

The float valve seat diameter depends upon the fuel pump pressure and how much power the engine makes.

Be careful lowering the float level to stop the flooding out of the vent lines at low engine speeds. This will sometimes keep the float valve from fully opening when fuel flow needs to high at high RPMs.

I looked up "Turbo Crank" in my two stroke dictionary. The other way of spelling "Turbo Crank" was "Snake Oil".

Kyle T - April 6, 2013 02:12 AM (GMT)
A chrome plated cylinder MUST use a soft iron ring. A chrome ring running on a chrome bore will ruin each other in a matter of minutes.

Nikisil plating is the best process because you can run a chrome faced ring on it.

Nikasil plating over the top of an aluminum offers many advantages.

1. Superior heat dissipation
2. The miss-match between an iron sleeve and port is eliminated.
3. Cylinder ware is reduces because the Nikasil is very hard.
4. There is a very slight reduction in friction.

I do not recommend plating an iron bore unless you are out of bore sizes. Plating the last bore will extend the life of the last bore a little. There are not any heat transfer advantages to plating an iron bore.

The only advantage plating the bore on an iron cylinder

The gearing depends upon the type of drag racing and the type of surface you are racing on. If you are racing in the dirt, sand, or hill racing, gear it to produce the best acceleration before the finish line. If you are racing on the pavement, gear it for the highest top speed.

I use every tool available, commercial software, home grown software, and 35 + years of mechanical engineering experience when I design a pipe for a new engine. Using all of these tools just gives me a starting point for the first pipe. The performance of the first few pipes of a new design is usually an embarrassment to me even with all of the experience I have in designing engines and exhaust systems.

Pipe development requires perseverance, patients and a lot of testing to get a pipe that works well.

I have never had a CR 500 Honda or a KX500 with radical porting, a stock pipe or any of the big name aftermarket moto-cross in frame pipes, make over 60 HP on my dyno. There is not space on a 500cc moto-cross bike to accommodate a pipe that can easily add 10 to 20 HP to these bikes. The LT 500 has ample space for any size or shape pipe you want to hang on her.

A LT 500 with the air box lid removed, a 41 or larger carburetor, stock ports, a head with the squish set, a large volume pipe like the Q Pipe, Aaen or Hall pipe will usually make 57 to 60 HP on my rear wheel dyno. Add a little port work to a LT 500 and making over 65 hp is a no brainer.

There is usually less than a 3 % gain when Cryo treating every thing in the engine. The NASCAR guys CRYO treat the tranny parts, de-burr everything and polish the load carrying face of the gears.

Engineers typically expect about a 2 to 3 % power loss each time power is transmitted through two gears meshing. A constant mesh motorcycle transmission usually consumes less than 1 % for all of the other gears not transmitting any power. Now lets add up how much power is typically consumed from the end of the crank to the rear axle.

Crankshaft pinion to clutch ring gear 2 to 4 %
Only one gear set in the transmission transmits power at any one time 2 to 4 %
All of the other gears in the transmission meshing but not transmitting power 1 %
A well lubricated chain that is broken in and running on new sprockets has about a 3 % power loss.

Adding all of the above losses, the power loss from the crankshaft to the rear wheel on a typical motorcycle is 8 % to 12 %. On a 60 hp engine the alleged $24,000.00 NASCAR treatment will buy you maybe 1.8 HP if the NASCAR magic was even good for a 3 % power gain.

I can think of a lot of easy ways to find 2 hp on any 500cc 60 HP single cylinder two stroke engine for a lot less than $24,000.00.

The CRYO treating is something that is done to increase strength or change the temper of the metal. It does not to reduce friction.

The deburring and polishing of the teeth reduces the friction a little bit. NASCAR is so competitive and so well funded, they will spend the money to get less than a 1% power increase.

The weight only affects the acceleration portion of a drag race. Weight has very little effect on a top speed pass.

The aerodynamics of the rider, quad or bike and the engine power at top speed is what determines the top speed.

The highest top speed will be attained when geared so that the top speed and peak HP occurs simultaneously.

If the gearing is not optimized, the highest top speed will occur on the vehicle that has the highest over-rev HP.

You can run it a 40:1 but I would not recommend than lean of an oil ratio on any engine that is run wide open for any longer than a couple of seconds at a time. How you operate the engine determines the oil ratio needed. Two strokes can be run at 100:1 but the fuse will be considerably shorter.

Originally Posted by PoWn3d_0704
.................I believe I can get just a bit more power out of that.
I hope you really do not believe that a two stroke will develop more power as the oil ratio is made leaner. If this theory is correct, at what ratio does the engine develop the most power?

There is less power available at 40:1 than at 30:1. There is more power at 20:1 than at 30:1 and there is more power at 15:1 than at 20:1.

That whole area of the case is real thin for about 2 inches in every direction around the left rear stud. Why are you having detonation problems? Detonation problems are always a result of your ignition-timing curve, fuel system, combustion chamber design or pipe design. It could be in anyone of these areas or a combination of these areas.

Any of the good carb cleaners that will actually clean the inside of the fuel passage ways, will dissolves gaskets, floats, and any rubber parts. Brake clean and carb cleaner in a spray can will not usually keep the areas of the carb that need cleaning wet with the cleaner long enough to do much good. The good carb cleaners are dangerous and the parts usually have to be put in a vat of it to really get everything clean.

We clean carbs every week that look spotless on the outside of the carb and on the inside the float bowl but there is still thin layer of varnish that is somewhere in the fuel passage ways or on the inside of the jets. The difference in the inside diameter of a main jet is usually less than .001" from one size jet to the next size.

It is not uncommon to find jets that have enough build up on the inside hole through the jet to flow 5 sizes leaner that what the jet was when it was new.


The fuel passage ways are very small in the low speed circuits in a four stroke. Any varnish in the jets or fuel passage ways can make the idle real lean. The needle jets also ware and can make the idle through 1/2 throttle real rich.

Stock 1988 to 1990 OEM carb, stock air box, aftermarket pipe without spark arrestor.

Jet Needle 6DK3 in the 2nd or 3rd clip position

Needle Jet always use the 389 series R-0 to R-2 for drag racing only
R-2 to R-6 for trail and dune riding. Use the richer needle jet if you spend more than a few seconds at a time at 1/8 to 1/2 throttle opening while the engine is running at high RPM

Pilot jet 22.5 to 25

Airscrew 1 1/2 turns from closed

3.5 needle seat

4.0 slide

Air correction jet removed

Stock choke jet

Lid on the air box, use 350 to 400 main jet

Air box lid removed, use a 380 to 500 main jet……….. depends upon type of air filter and air filter oil.

High airflow intake filter systems, use 500 to 680 main jet

An o-ring head does not need to have thread pulling, bolt stretching, stud breaking torque to provide the clamping force that is required to make a conventional head gasket or copper gasket seal.

An o-ring head will easily hold 2000 psi with the head nuts finger tight. A high HP LT 500 makes under 1000 psi peak cylinder pressure. 1000 psi combustion pressure will cause some stud stretch and lift the head off of the cylinder head gasket surface when the head nuts are finger tight.

When the head lifts off of the head gasket surface the o-ring will see the fire in the combustion chamber and o-ring failure will result in a very short time. Using 15 ft-lb to 17 ft-lb on a 10mm stud and 18ft-lb to 20ft-lb on a 8mm stud will put enough tension on the studs to prevent the head from lifting off of the head gasket surface. Applying any more torque than 20 ft-lbs contributes to the distortion of the bore. Oversized studs everyone thinks is necessary are not necessary for an o-ring to seal.

Many of the cylinders we get are really screwed up from the poor workmanship used when installing oversized studs. Do not attempt to install oversized studs, install heli-coils or any other type of thread repair unless you have a mill that is trammed and you are proficient at using a mill. Most drill presses are not trammed square enough to do the head stud repair and be able to get the head over the studs without drilling the bolt holes larger in the head.

Drilling the bolt holes larger in the head makes it very difficult to center the head over the bore. A head that is not centered over the bore may be more prone to having detonation problems.

It changes the slope of the fuel curve through the main jet. It takes a dyno and fuel flow instrumentation to properly find the optimum size air correction jet for a given engine package. The majority of the LT 500s need the jet removed or a 2.0 size jet installed.

The clutch plate is aluminum with kevlar friction material bonded to it.

The bridge is there to improve piston life. If the port is shaped correctly and not to wide, if usually does not shorten the piston life significantly. The bridge on the small reed cylinder is famous for cracking, especially if someone has made the bridge more narrow or tried to knife edge it. Sometimes the small reed cylinder intake bridge will crack when the bore sizes are beyond 87.5mm and the piston to cylinder clearances get too loose.

The shape of your intake looks ok but I can not tell how wide the port is without measuring it.

Your sleeve will not be too thin with a .080" oversized piston. You may need to use a head gasket that is made for the larger bores. I think the .080" piston may hit the OEM head gasket.

50 mm to 52 mm chordal width at the widest point is stock. I do not like too make the intake port wider than 54 mm when the bridge is removed unless the engine is a drag engine and short piston life is expected.

I have rebuilt some engines that had mild port work with the bridge removed and the intake port was 61mm wide. The pistons try to fall into the intake port when they are wider than 55 or so mm with the bridge is removed. The intake port does not need to be very big for most engines unless it is a very radical engine package.

Yes it does change the lever ratio. It also reduces the distance the pressure plate travels when the clutch is disengaged. I have seen and tried many different devices that alter the lever ratios over the years. The leverage changing devices are not rocket science. You have to give up pressure plate travel for reduced effort at the clutch lever. Reduced pressure plate travels usually results in a clutch that will not full disengage and cause the bike to move when you rev the engine or it may kill the engine when drop in into first gear.

Big power = heavy duty springs in clutch

Heavy duty springs = much more effort at the clutch lever

Much effort at the clutch lever = Strong forearm

Strong forearm = real men


Wimps should not ride Quadracers

Acetone is the best cleaner to use to get the oil off of aluminum after the surface has been ground with a carbide burr to get "a bright clean aluminum surface". Acetone leaves the least residuals on an aluminum surface. Brake cleaner, carb cleaner etc. leaves a lot of carbon residuals and makes the aluminum weld like it is dirty even though it looks clean.

Use Heli-coils in aluminum and magnesium. I do not have time at the moment to talk about why I do not like time-serts keen-serts etc. I will try to post an explanation tonight or in the morning. Use a mill to do any type of drilling or tapping for head stud repair!!!!!!!!!!!!!!!!!!!!!!!!!!!

Watch the time-sert video that Tex posted a link. Watch the time-sert guy drill the hole at an angle with a hand drill. After he taps the hole, he doesn’t even blow the chips out of the hole or wash out the cutting fluid before installing the insert. I think that this video should have been named “Time-serts for Dummies”. Videos like this is one of the reasons the average guy does not have successful thread repair.

I have never seen a heil-coil back out of a hole or stick to a bolt or stud when it is removed. I have removed hundreds of bolts with a time-sert stuck to the bolt. The self-expanding feature the video guy was talking about apparently does not work 100% of the time. Staking, expanding a time-sert, using loctite does not keep the time-sert from eventually getting loose in the hole.


Loctite is not necessary when the proper thread diameter, thread pitch and length of bolt is used. If you are tempted to use loctite to keep something tight you need to study the problem and correct the current problem and not create future problems

We have to charge customers for the extra time it takes us to work on their bikes because of the improper use of loctite. We recently had one of these bikes where the guy used “red” bearing and stud mount loctite on everything. I know the previous mechanic had good intentions and was trying to be very through, but it cost the owner almost $300.00 more that than it should have to repair all the broken bolts and stripped threads in the aluminum.

The expansion rate of a one-piece steel time-sert is not same as the aluminum that it is screwed into. The heli-coil resembles a spring; this feature allows it to expand length wise and diameter wise with the aluminum it is screwed into.

Like Tex said, almost every threaded hole in aluminum or magnesium in the aero-space industry has a heli-coil install in it when the part was manufactured.

Oversized holes for the insert tap is the # one problem with any insert repair. A hole that is a few thousands too large severely reduces the torque holding ability of the insert repair. Using a hand drill like the guy in the time-sert video, will always drill a hole that is slightly larger than the drill he was using. A chuck that wobbles a few thousands will also drill an oversized hole even when the correct diameter drill is used. Using a hand-sharpened drill of the correct size will always drill a hole that is larger than the diameter of the drill.

I use the mill to drill the hole with a bit that is about .010” undersized, and then I use the correct diameter drill to finish the hole to the recommended diameter. I use the mill to hold, start the tap, and cut at least ¾ of the depth of the threads by turning the spindle of the mill by hand.

Using a heli-coil insert that is too short is another problem for failed thread repairs. Contrary to most engineering books I use an insert that has a length that is at least 2 bolt diameters in length. For head stud repair, the insert should engage every thread that screws into the cylinder.

A 10mm x 1.25 threaded hole for head bolts will not strip unless it has been over torqued or one of the above cautions were not observed when the thread repair was made.!!!!!!!!!! A 8mm x 1.25 head stud hole will also not strip unless it was over-torqued!!!!!

Guys over torque the head bolts trying to stop conventional and copper head gaskets from leaking. These problems are head and head gasket design problems not a problem of using head bolts whose diameter are too small.

Measure the main bearing pockets. Many of the pockets we measure are loose enough for the outside bearing race to spin in the case but have a lip that keeps the bearing from falling out of the case. Because you have to press the bearings out of the cases is NOT an indication that the bearing pockets are tight where it counts.

There should be .0015" to .0020" interference fit at room temperature for the bearings to be tight when the cases, bearings and crankshaft are up to operating temperature. If there are pits on the bearings or bearing pocket surface the pockets need to be re-sleeved.

There is not any advantage to re-sleeving bearing pockets that are tight. All LT 500 bearing pockets will eventually get loose given enough hard run time. Flex in the crankshaft causes the bearing pockets to ware out. The bearing pockets on some of the original cases came through a little on the loose side and it did not take long for the bearings to spin or fret in the original pocket.

Pockets that have been re-sleeved will eventually get loose with enough mileage and or when the power level goes up. The material used, bronze, brass, aluminum, steel, plastic or iron does not guarantee they will never get loose again. The type of material used does make it possible and reduces the cost if they get loose the second time.

This is what we do when we repair/re-enforce the ears on a LT500 cylinder

1. Remove all hardware from the cylinder, (power valves, studs etc.)
2. Prepare cracked area and weld the crack.
3. Prepare the area where the ears will be reinforced
4. Make a billet pieces to weld onto the cylinder to give it added strength
5. Weld billet pieces to cylinder
6. Machine base nut seating surface
7. Grind welds smooth and sand blast cylinder
8. Machine base gasket surface
9. Machine head gasket surface
10. Machine reed gasket surface
11. Install studs
12. Bore cylinder

There are cast iron inserts on both sides of the cases from the factory. The mag side has a iron insert, but it is not obvious because it has aluminum cast around it. Check it with a magnet. The original cast iron inserts are just fine if they have the correct interference fit. Aluminum inserts are fine if they are tight, they just do not last as long as some other insert materials.

How are these guys measuring their speed. Are they using a radar gun, GPS or one of the handlebar mounted digital speedometers.
I have found that that a radar gun gives the most accurate testing results followed by a GPS and lastly by the dash mounted devices

The digital speedometers require user information like tire size, and overall gear ratio in 5th gear. The speedometer measures the engine RPM and uses the user information to calculate the speed. The speedometer does not know what transmission gear you are using; all it knows is the RPM the engine is turning.

There are a couple of easy ways to "cheat" and make the speedometer display any speed you desire.

1. Input an incorrect tire circumference, or gear ratio.
2. Allow the engine to rev higher in any of the lower gears than it will pull in 5th gear.
3. Not use a resistor spark plug cap or resistor spark plug to give erroneous RPM readings.

If you over-rev the engine to 9800 RPM in one of the lower gears and have the speedometer set to the tell-tale mode, the speedometer remembers the highest RPM it saw since it was last re-set. The speedometer uses the maximum RPM and user information and assumes the transmission was in 5th gear to calculate a top speed.

Compression ratio is one of the most understood engine specifications. It does not have a huge effect on power in a two stroke like it does in a 4 stroke, but can have a huge effect on detonation in two and four strokes. I will write more about compression ratio when I have some time. I need to try to think of a way to try to scratch the surface on the topic without writing many pages.


I recently finished a new adapter plate design for the big reed V2. It will not allow the screws to fall out and it is slightly thicker than the original V Force and Tudors adapter plates. I have about 15 or 20 of these in stock.

Do not use Loctite on the threads that screw into the cylinder. I would not use more that about 5 to 10 ft-lb of torque to install the studs into the cylinder. Using more torque that 10 ft-lbs will distort the bore and make a bulge in the bore in the region of each stud. Using Loctite on the threads may cause damage to the aluminum threads if the studs are removed for future head gasket surface maintenance.

I do not like to weld the crank pins on ANY crank unless the press fit on the pin is substandard. If the crankpin holes are good and the press fit it tight, it is not necessary to weld the pins. Welding the crank pin reduces the number of GOOD rebuilds you can do to a set of crank halves.

If the bearing pockets are within specifications, there is not any advantage to re-sleeving the bearing pockets other than reducing the thickness of YOUR wallet

OEM head gaskets are superior to the after market head gaskets. O-ring heads do not distort the bore as much as conventional head gaskets and are cheaper than OEM gaskets once you pay for having the necessary welding and machine work that is necessary to o-ring most two strokes heads.

I have not observed any abnormal ware on the wrist pin bearings or on the wrist pin bearing end of the con rod on engines that did not have a hole or port in the piston intake skirt when running good two stroke oil at a ratio suited for your riding style.

There is not universal agreement on what are "proper head specifications", "stockish porting" "decent pipe" etc. are. Every engine builder has different engine specifications for different engine packages.

The CCs in the head, is not what determines the octane rating a particular engine package needs. It is the density, temperature and pressure of the trapped charge in the cylinder near the point of ignition that really determines the required octane level of the fuel. The squish clearance and squish angle may also need to be different for different engine packages.

I have seen some poor engine combinations of pipe and ports that could run reliably on pump premium at over 200 psi cranking pressure and other well developed engine packages that only have 130 psi cranking pressure and need over 110 octane.

I have silencers catch fire all of the time when running bikes on the dyno. It usually happens on bikes that are not run hard and have the packing saturated with oil. Engines that are run hard all of the time will not have this problem.

When you run an engine hard for a few minutes, the exhaust temperature at the silencer can easily go over 800 deg. F. This is hot enough to ignite the old two stoke oil that has accumulated in the packing when you let off of the throttle. The inside of the silencer will not burn as long as you are on the throttle because there is not enough oxygen left over to support the combustion of the old hot oil. Oxygen laden outside air is sucked through the silencer into the expansion chamber every time you close the throttle. If the oil in the silencer is hot enough it will burn when the oxygen is supplied.

The head pipe turning orange on a four-stroke is not unusual when we are dyno testing even with the high velocity fans flowing over the exhaust system. It is unusual on a two stroke for the head pipe to turn orange and sparks to be emitted when the bike is at high speed or on the dyno when a lot of air is blowing over the head pipe.

The head pipe turning orange is usually an indication of one or a combination of the following.

1. The engine is being "revved" way past the power peak.
2. The ignition timing is too retarded at the RPM that the head pipe turns orange.
3. The air fuel ratio may be a little lean.
4. The exhaust is too restricted at the stinger (stinger ID is too small)
5. The silencer core is broken and restricting the flow.
6. The spark arrestor screen needs cleaning.

High temperature exhaust passing through the silencer raises the temperature of the packing and the charred oily residue forming small glowing little charcoal nuggets. The high velocity exhaust dislodges these and blows them out to the atmosphere. The instant the hot nuggets are exposed to the oxygen in the atmosphere, they ignite and make cool looking little tracer like sparks.

Ceramic bearings decrease the friction very little in an engine. They are really expensive and I do not think that they give much bang for the buck. Tuning your engine to within one jet size of optimum will give you more power than $500.00 spent on ceramic bearings.

Using the head stay helps reduce frame breakage under the fuel tank. Using the head stay increases the stress on the cylinder, head and cases if you do jumping or have lousy suspension. Which is cheaper, a new frame or converting the head to an o-ring type seals? New OEM heads and cool heads are still available, new OEM frames are no longer available. Most heads with copper head gaskets have trouble sealing even when the head stay is removed. I have not had problems with the heads leaking when they are o-ringed and using the head stay.

The choice of running the head stay is a personal decision each owner has to make. It is a matter of deciding which components are least expensive to replace if they break.

I use O2 sensors all of the time when tuning 4 strokes. They are a real time saver to get you in the ballpark on jetting and then use the dyno to tell you the best power setting on jetting or fuel injection. Any shop that tunes for A/F ratio only does not need a dyno. Just get an A/F meter and ride and tune it yourself. I want the engine to produce max power regardless of what an O2 sensor says. You need a dyno or some means to tell when your engine is getting the fuel that produces the maximum power. Not all engines produce max power at the same A/F ratio. Some engines and exhaust system combinations will make best power when the O2 sensor readings are in the low 12:1 ratio and other engine will be in the high 13s to low 14s:1 ratio when producing maximum power.

A dyno shop that tries to sell you on the merits of using an O2 sensor when jetting a two stroke is a shop that does not have the necessary experience and has a very shallow understanding of how two strokes really work. I know this is contrary to what all of the dyno operators that have been to the dyno tuning school in Las Vegas have been blindly taught. The professors at the University of Air Fuel Ratios are not engine designers they are in the business of selling dynos and tuning hardware to the average mechanic.

Please search this site for information I posted recently touching on some of the “whys” O2 sensors ARE NOT a very useful tool for tuning two strokes. I will be happy to answer questions after you read and understand a few more of the “basics” of why an O2 sensor cannot really measure the byproducts of combustion in a two stroke.

Guys -

I think its good information on jetting the off throttle - low speed jetting on a 2 Stroke.

#1. Wont a 2 Stroke (after warmed up, after running WOT) hang up a little before it returns to it normal idle speed? What is a long time?

ALSO - does a rich main jet contribute to high idle speed after a run and returning to idle?

#2. If it does hang up for a period of time and has the "ring ding dings" - what is the condition of the jetting? I assume its rich and adjusting the air screw will help tune this.
It is not uncommon for the large displacement single cylinder two-strokes to ring da ding a little just before they return to an idle RPM. The engine RPMs should not hang up at a higher RPM before slowly returning to idle. Some two strokes will hang when very hot and the fuel octane is too low. These two conditions are usually a combinations of inherit engine design and a lean condition.

All of the surfaces inside the crankcase are slightly wetted with fuel and oil at all times. “How wet these surfaces are depends upon the throttle opening, the engine RPM and how long the engine has been operating at these three conditions. These surfaces include the transfer port walls, reed cavity, crankshaft and the cases surrounding the crankshaft. At full throttle the thickness of the wet layer diminishes as the RPM increases and stabilizes after a few seconds of wide-open throttle. When the throttle is closed the wet layer thickness increases until it cannot hold any more fuel and oil and sheds the excess fuel into the air stream after the layer thickness has stabilized.

All of the fuel that leaves the carburetor on a given engine revolution does not make it to the combustion chamber when the throttle is closes and the RPMs are decelerating. Some of the fuel is used to increase the thickness of the wet layer on the surfaces inside the crankcase while the rest makes its way to the combustion chamber. While the layer of wetness increases in thickness, the combustion process experiences a lean condition and the ring da dings continue until the layer thickness stabilizes and the engine starts to idle normally if the pilot jet and air screw are in the ballpark.

After the throttle has been closed for a number of engine revolutions and the throttle is opened, the layer of wetness starts to diminish and the fuel from this layer is added to the fuel that is coming from the carburetor on the current engine revolution. During the time the layer is “drying out” the combustion process is experiencing a slightly richer mixture than what it would be getting after the surface thickness has stabilized. This is what is occurring when a two-stroke is “loaded up” and begins to run well after a few seconds of full throttle. The mixture from the carburetor did not change from the time the throttle was first opened and the engine had a rich misfire until it “cleaned out” or began to run well. The additional fuel from the wet surface made the overall mixture too rich when the throttle was first opened

The above phenomenon continually occurs and with different degrees as we open and close the throttle as the engine RPM varies as we ride.

If it does hang up for a period of time and has the "ring ding dings, it is lean while it is has the ring da dings. It is NOT RICH while it has the ring dings dings.

On deceleration the needle jet and the pilot circuit supplies fuel to the engine. On high RPM deceleration the needle jet supplies more fuel than the pilot circuit. The amount of fuel from the needle jet diminishes as the RPM decreases and eventually the pilot circuit is responsible for the idle mixture. The pilot circuit supplies the majority of the fuel to the engine after the engine idle speed stabilizes.

An engine that “hangs” at the higher RPMs has a lean condition that needs to be corrected! The lean condition can be the result of any one or a combination of the following:
1. An air leak
2. The needle jet is too small
3. A worn slide or carb body where the slide seals against the carb body.
4. A carb that has been bored too large or bored off center. # 3 and # 4 will produce similar symptoms.
5. Pilot jet is too small or one or more of the pilot transition holes is plugged or partially blocked.
6. Airscrew is set extremely lean or the airscrew is missing.

Four-strokes experience the same problems with port wall wetting but the surface area of the intake port in a four-stroke is much less than the surface area in a two-stroke crankcase. Four-stroke heads typically run much hotter than the ports and crankcase of a two-stroke. The additional heat in a four-stroke head also reduces the thickness of the wet layer on the intake port walls.

Some inconsistent carburetion problems are actually due to the wetting phenomena on the crankcase and port surfaces.

Water wetter does not seem to have the corrosion protection and lubricity for the water plump seal that the antifreeze coolants have. I only use water wetter in engines that the rules will not allow antifreeze. I have not seen enough heat transfer benefit from the water wetter to out weigh the slight increase in corrosion and water pump seal problems on the engines I have worked on.

The list of specifications is pretty vague as what has been done to each of the listed components.

There is more than one way to shape a combustion chamber and have the same volume. Different engine builders do different things to the head for different types of engine builds.

The different Alloy inlets also run different, depending on the shape of the air horn and type of air filter.

Different engine builders do different things to the rubber manifold that connects the carb to the reed.

If you were to run a 1987 or 1988 stock cylinder with all of the above components that I had modified for the below porting setup and used the Q pipe and silencer, it would make about 60 HP to the rear wheels on my dyno.

Using the same above components with the "right" porting and the Q pipe and silencer, I would see around 72 to 78 HP on a small reed cylinder and about 76 to 80 on a big reed cylinder.

The amount of power a port job will add to the other components, depends upon what components you have. Adding porting to a package that has all of my drag components will add about 30 HP.

Large reed cylinder, 88.5 mm bore, 86.0 mm stroke, HPR 19 pipe and silencer, 44 Mikuni round slide, methanol,

RPM Torque ft-lb
5500 52
6000 58
6500 61
7000 67
7500 71
8000 66

Any bearing that has the same dimensions as the RM bearing will work. Bearing manufactures use different materials and designs of the bearing cage. The design of the Suzuki bearings have been tested and proven. Why risk destroying your engine just to save a few dollars. Suzuki's suggested retail price is even cheaper than the Wiseco bearing.

The OEM washers are junk.

Pressures check the engine with the clutch cover off before you remove the seal or crank nut. DO NOT JUST ASSUME THE SEAL IS LEAKING!!!!!! If the right crank seal is leaking it will show if you spray some soapy water on the seal area. If the crank seal is not leaking it may be leaking between the case halves. If the connecting rod bearing has failed sometime in the past, the cases could be cracked or distorted where the rod was rubbing the cases.

The piston crown shows extremely high exhaust temperature; a ring of detonation etching and a crater in the center.

The edge of the piston that is burned away next to the exhaust port was from the high exhaust temperature.

High piston temperature on the exhaust port side of the piston probably caused the detonation. The high piston temperature may have been due to an air leak or some problems in the fuel system. The detonation can also be cause by ignition timing that is too advanced, low octane fuel, an exhaust system that is too restrictive or a bad combustion chamber design.

Detonation caused the spark to start glowing and caused pre-ignition. Pre-ignition caused run away detonation and the piston crown rose high enough to expand the piston to the point that the piston clearance disappeared and the piston tried to weld its self to the cylinder wall. The molten puddle on the surface of the center of the piston will also cause pre-ignition. All of the damage on the piston crown happened in less than 10 to 15 seconds.

The location of the etching ring cause from detonation has me concerned. Detonation etching is usually concentrated along the edge of the piston close to the cylinder wall. The ring of etching is located approximately at the intersection of the squish band and combustion chamber. This may be the result of a bad combustion chamber design or there may be many things in your basic engine package that is not right.

We build silencers and have 3 mandrel tube benders. I have U-bends, J-bends 45degree and 90 degree bends if you want to make your own mid pipe.

We can custom make any thing you want but the design work and bender setup charge makes one off pieces expensive. If you are making a hundred of the same thing the set up charge spread out over a hundred pieces doesn't add much cost to each part.

The majority of the high cost specialty coolants are just highly marketed snake oil and do produce the results promised. Like Deebo said "Just use antifreeze. If you're running hot, something isn't right." Save yourself the money and just use a name brand automotive antifreeze that is designed for aluminum engines and cooling systems. I do not know of any antifreeze that is on the marked that is not for aluminum engines.

Coolant/antifreeze is not rocket science. We have had about a hundred years of research for engine coolant chemistry. There has not been any magical coolants been developed in 30 years. There have been a lot of little companies that come to the racing community with their "new unique high tech chemistry". They are like shooting stars. They typically disappear as quickly as they appeared.

Do not plug the weep hole. The weep hole was created to keep coolant from being forced into the transmission when coolant leaks past the impellor area. 90 percent of the weep hole leaks are because of coolant leaking between the impellor bolt head sealing washer and the impellor not the water pump seal. Replacing the impellor and sealing washer or modifying the old impellor usually fixes the leaking problem on the LT 250s and LT 500s.

It sounds like you have it just about right for general purpose riding. I would leave it alone.

Making the pilot jet leaner, increasing the diameter of the straight portion of the needle or installing a leaner slide can eliminate the rat-tat-tat in the zero to about 3/8 throttle opening at low engine RPMs and light loads. Eliminating the rat-tat-tat below ¼ throttle will make it more prone to burn the exhaust side edge off of the piston when running it at less than ½ throttle and higher RPMs where the pipe is working. The magic combination of pilot jet, needle jet, needle straight portion diameter and slide cut away are VERY important to having a reliable engine.

Smaller inside silencer diameters, poorly designed spark arrestors and or dirty spark arrestors can make an engine run like it is rich while sometimes raising piston crown temperatures to the point of piston crown failure or seizures. We see a lot of piston failures that are the result of poorly designed spark arrestors and or sloppy welding at the junction of the tail cone and stinger. A little weld bugger inside the pipe at this junction is many time all it takes to overheat the piston crown to the point of failure.

Highly modified engines are VERY prone to high RPM less than ½ throttle piston crown failures. Highly modified two strokes should not be operated at high RPM at small throttle openings for more that a couple of seconds at a time. There is an inherent design problem all two strokes have and is related to incomplete scavenging at partial throttle when the engine RPM is high enough that the pipe is assisting the breathing of the engine. Changing the air fuel mixture cannot cure this inherent design problem. The incomplete scavenging problem increases as the power level of the engine goes up. It is not something that can be tuned out of a high performance two-stroke. This is the primary reason that high performance two-stroke street bikes burn piston crowns at highway speeds and do not make reliable transportation. The air fuel mixture can be made excessively rich at small throttle openings so the engine runs so lousy that it cannot hurt the piston but who wants to ride something like that to work.

Two stroke exhaust pipes need the proper amount of restriction. Adding a little more restriction than the optimum will not usually hurt peak power. Most of the time, adding a little more restriction than optimum amount will give slightly more over-rev (Power that does not decline as rapidly after the power peak). Drag racing pipes are typically slightly over restricted and will be ok for 3 to 10 second blast of full throttle but may produce repeated piston failures when used for an application where the throttle is open for longer periods of time.

How a high performance two-stroke is ridden can have as much to do with piston crown failures as the jets in the carburetor. I have seen thousands of piston crown failures over the years and the jetting associated with those failures. I know how to ride a bike to make it live with lean carburetor settings or I can make a piston fail in less than 30 seconds even when carburetor settings are considered rich enough to be safe.

I am sorry for taking so much time to answer what appears to be a simple question to most two-stroke owners. I have tried to give a general answer to a complex problem that would require volumes of text to explain the science behind the problem. I have not seen anyone else address this very important issue on this forum.

Put the special rubber sealing washer that the book calls for. If the end of the shaft protrudes above the impellor, the rubber washer will not seal properly against the impellor. Replace the impellor or grind off the end of the shaft so that it is about .010" below the surface of the impellor where the rubber washer seals against the impellor. Fix it properly and do not use a band-aid by putting ANY of the coolant system sealers like alumina seal, bars leak etc. The stop leaks hinder heat transfer from the cylinder and head to the coolant and then hinders the heat transfer from the coolant to the radiator.

Because Suzuki does not pressure check for pinholes in the cylinder coolant passageways and they don't check the radiator for leaks on the production line. The cooling system is more than sufficient for a 45 HP stock engine and reducing the efficiency a little will not over heat a stock engine. The cooling system is borderline adequate for the highly modified LT500s.

Anytime you increase the power 25 to 100 % on anything, the original cooling system will not usually be adequate so we do not want to put anything in the coolant that will make the cooling system less efficient.

The automobile manufactures test all types of coolant for heat transfer, corrosion protection, freezing protection, how often the coolant needs to be changed and for cost verses effectiveness.

The cost verses effectiveness for engine ice is obviously not there or it would come in all of the new cars. Most of the chemicals that we use in our toys are JUST repackaged automotive products. The high cost for the chemicals we pour into out toys is mostly of the enormous amount of money they spend trying to convince (brain wash) us to give our baby the best money can buy, not because they have developed some magical formulation or additive that they put in the potion that we give our pride and joy.

Ring ding ding on deceleration is not octane related. It is lack of fuel and incomplete scavenging that causes ring ding ding on decel.

Both spark plugs are exposed to the same temperatures and mixture. If one plug is fowled the other one will be in similar condition. The extra spark plug holes were for a compression release.

The mechanical and rubber oil seal produce a little resistance to rotation of the shaft.

First, make sure that your engine does not have any huge air leaks. I would work on finding the right combination of pilot and needle jet for your engine. The theoretical graphs that carburetor manufactures publish that show which fuel circuit is working at different throttle positions does not tell the real story.

The pilot jet is connected to two holes where the fuel is supplied to the air stream. The idle hole is down stream from the slide and the transition hole is between the front edge of the slide and the needle. The idle hole supplies most of the fuel when the engine is at a steady idle because the vacuum is much higher at the idle hole than at the transition hole when the throttle is closed. The transition hole begins supplying fuel into the air stream when the air velocity over the hole is high enough to produce enough vacuum to pull fuel through it. The needle jet also begins to supply fuel when the air velocity over the needle jet is high enough to produce enough vacuum to pull fuel through it.

The pilot jet supplies most of the fuel the engine is using through the idle hole when the engine RPM has stabilized and has been at an idle for a few seconds. When the throttle is closed and the engine is at high RPM, fuel is supplied to the engine from the idle hole, transition hole and needle jet as the engine decelerates. At high RPM and closed throttle, the air speed over the transition hole and needle jet is still high enough to pull fuel from these three circuits. As the RPM diminishes the air velocity over the needle jet hole will eventually become low enough fuel flow from the needle jet stops. Fuel flow from the transition hole will eventually stop when the RPM drops to a point slightly higher than an idle.

If the proper proportions of needle jet size, pilot jet and proper sizing of the transition and idle hole to keep the ring ding ding to a minimum,.

The design of the exhaust system, combustion chamber shape and port angles can also have a pronounced effect on reducing the ring ding ding on a two stroke engine.

If you have a Mikuni you will have to work with the pilot and needle jet to reduce the ring ding ding. The needle taper and clip position has NOTHING to do with fuel flow when the throttle is closed. At closed throttle the fuel flow is controlled by the pilot and flow area between the needle and the needle jet.

If you have a Keihin carburetor you have to select a needle that has a smaller diameter on the straight portion of the needle. The Keihin carbs do not have a replaceable needle jet. This is one of the reasons I do not like Keihin carbs. The needle moving up and down inside the needle jet wares the needle jet and makes the carb get richer as it gets older. You have to keep replacing the carb or keep changing to a needle that has a larger straight portion on the needle to keep the mixture consistent in the zero to about half throttle position.

It is really disappointing reading this article and seeing the level of understanding the author has on detonation, volumetric efficiency, the combustion process, fuel chemistry, octane rating, and what lead in the fuel does.

The above article is one of the worst articles about detonation I have read. I hope the author is not the guy doing the work on the heads. I wish I had time to explain what detonation is, what really causes it and how to prevent it. It would take many pages just to scratch the surface on the topic of detonation. Keep searching, there are articles out there that are much more informative about detonation. I think Kevin Cameron has a good articles named "Deto".

Some of the stuff written about twin plugs for the primitive combustion chambers on Harleys and some of the old air craft engines is ok but what was written about twin plugs does not have much application for two stroke cylinder heads that have properly shaped squish band and combustion chamber on a loop scavenged two stroke.

I know that the twin ignitions are required on two and four stroke aircraft engines for safety.

I have been designing engines for companies and the modifying existing engines for the public for over 35 years. My experience has been: When we had to install a second plug in a two stroke head to stop detonation we were putting a band-aid on a bad engine design.

Poorly designed four stroke heads sometimes need multiple spark plugs.

The 125 GP road racing bikes made close to 60 Hp and the 500 GP bikes made over 200 HP on gasoline with single spark plug heads. None of the state of the art Aprillias, Hondas, or Yamahas factory grand Prix 125s, 250s and 500 used twin ignition or twin spark plug heads. We would have used more than one spark plug per cylinder if it produced more power, made the engine more reliable or reduced incycle pressure variations. Money was not an object on engines at this level. Winning races was the central focus.

Dual spark plugs can help reduce emissions as well as reduce the octane requirements in FOUR STROKE HEADS.

The majority of the head surface in a four stroke head is used to get air in and out of the cylinder. Valve placement and the number of valves is one of the most important design criteria in a four stroke head. What space that is left over sometimes has quench areas. The quench areas in a four stroke head serves the same purpose as the squish area in a two stroke head. The combustion chamber shape in most four strokes does not have a smooth progression, the shape is not symmetric and there is not enough quench area to control detonation. Hot valves also promote detonation. Single spark placement is often not symmetric in 2 valve heads and is often placed in the space left over

Two stroke heads can be designed to place the spark plug in the optimum location within the combustion chamber. Two stroke heads can be designed to have the optimum amount of squish area that promotes the optimum flame speed. Two stroke heads can be designed to have a combustion chamber shape that controls the pressure rise and decay to promote a smooth impulse to the crankshaft. Two stroke heads are designed to promotes a very rapid burn, minimizes heat loss and have effective detonation control.

I am not trying to beat a dead horse but attempting to educate those on the forum of some of the major design considerations between two and four stroke combustion chambers.

When we o-ring a head the squish area has to be machined to yield the proper piston to head clearance. Sometimes the dome also has to be machined. The amount of material depends upon the length of the cylinder, base gasket thickness and the target compression ratio.

The head on Ebay should be able to be saved if it has never been machined.

On a 6 bolt (1987) head, I consider the head to be junk when the thickness is less than 16.0mm or about 0.630". The thickness measurement is measured from the head gasket surface to the surface where the head nut washers touch the head. The combustion pressure will flex the head enough to cause the head gasket to leak or allow the head to flex enough that the o-ring will "see the fire" and eventually fail.

The liquid cooled systems primarily function is to cool the torch. The secondary function is to keep the small power cord to the torches cool. If the power cord was not liquid cooled the power cord would have to be very large making the torch heavy and difficult to do control. I have melted the power leads many times when the liquid stopped flowing around the wire in the power cord on an old 600 amp welder I use to have. The 600 amp welder was hooked up directly to the garden hose.

My Miller 375 amp square wave machine has its own cooling system with a reservoir pump and radiator. I use prestone green automotive antifreeze at a 50/50 mix with water. I have two torches hooked up to the Miller. One torch is for under 100 amps and the other is good up to 400 amps of continuous welding. The cooling water and the gas flow to the torches are on a manifold that allows me to quickly switch from one torch to the other by turning two valves to direct the gas and water to the desired torch.

Sell the Z400 and buy a LTR450. We have been down this road and the Z400 will not stay together with big valves, porting, pipe, big bore, cam, and stroker crank when the power is increased to match that of a LTR450 with a pipe and air filter.

It will cost over $3000.00 to turn the Z400 into a grenade.

Did you get all that?

LordZilla87 - April 6, 2013 04:57 PM (GMT)
Good read, thanks for taking the time to post all that.

Kyle T - April 6, 2013 11:13 PM (GMT)
You're welcome LZ!

alkyzilla10 - April 9, 2013 05:48 PM (GMT)
Thanks Kyle!
Lot of "to the point" info right there....! I learned some stuff I had forgot about myself in that read.

Kyle T - April 9, 2013 06:33 PM (GMT)
You are also welcome Dale!

grkguy - April 12, 2013 01:59 PM (GMT)
took me 3 days to read all that, good post kyle

Kyle T - April 12, 2013 02:33 PM (GMT)
Good 3 days though huh? :D

qzillanut - April 12, 2013 03:50 PM (GMT)
Nice compilation

Kyle T - April 12, 2013 11:14 PM (GMT)
Yes it is. Jerry knows his stuff.

el diablo - April 13, 2013 08:36 AM (GMT)
Every answer to every question right there!

Kyle T - April 16, 2013 03:18 AM (GMT)
Not every. But damn close!

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