LT250 to 1986 RM250 Hybrid, Port differances

For anyone interested in doing an 86 RM250 to 87+ LT250 Hybrid, I have been doing research and got a hold of port maps for all three stock jugs (directly from Suzuki), 86 RM, 87LT, 88-92LT. The RM250 jug has basically the same intake porting as the 87LT jug, so obviously has better intake porting than the 88+ LT cylinders. The RM jug has way more transfer port area than any of the LT jugs, it would take a lot of porting on the LT's to match the stock RM transfer ports. The 86RM has roughly 8% (depending on how many decimals you want use and how you round off) more exhaust port area than the 88+ LT's. The RM exhaust port is also slightly taller (higher) than the 88+ LT250. The 87 LT jug is very close in exhaust port area to the RM. The disadvantage to the RM is that the exhaust port is oval and not bridged, so it imposes some restrictions on porting vs any year LT jug.

Bottom line is that, properly setup (ie pipe/reeds/carb etc), the stock RM jug should be a substantial power increase over any stock LT jug, including the 87, and is a direct bolt on. You also have the choice to use an FTZ YZ piston to eliminate the thrust washers, or any 87 LT piston, or an RM piston. But ultimately the 87 LT jug could be ported to provide more power (because of the non-bridged RM exhaust port), but it would take a lot of work on the transfer ports.

Just thought I would share.

Jim J

Hey, Hows that thing run, ....... I have seen a few mostly out of desperation....blown motors and NEEDed a cyl......... Hey, Hows that pipe work..... The one guy I know who had a good running Rm cylindered lt had a full custom pipe done to match the "porting".... after I talked to him he said he had more in getting the rm cyl rite than he would of an LT..... Hmmmmmm, spend money on a cylinder with a port setup that has no pipe designed for a that particular chassis......
gee I wonder why we dont see more of them if there such a hot set up........ prolly cause the guys that know tried it and found it aint the hot ticket........ Hmmmmm, did the rm really run and rev so hot or was it the fly wheel that made it feel fast...... rev.........

If your so knowledgable on the Lt's put up a post and lets see what ya got......

Oh ya let me know how that FTZ motor Runs......... I had two, reason I got the second one was the first one was pretty fair....... apparently they switched help....... cause the F'en carb was even bored backwards....for the second one..... wish I still had the origional....... oh ya the repinned piston is a little touchy they fall out usally at the wrong time......... but let us know how ya make out

Wow, I'm sorry Carl, I just thought I would post some information for anyone that might be considering using an '86 RM250 jug. I didn't realize all you guys with ported '87 LT250 jugs had custom pipes made to match the porting, that must make you're port job awfully expensive.


Jim J

You missed the point the Rm jug is the one that needs a custom pipe ......all the lt port jobs were done with a pipe in mind. And with Ftz be careful they did some good stuff................. long time ago...... but all shops switch help and lose knowledge in the cross over, unless they are a one man show....

First of all thanks for sharing your experience with FTZ, so far all I have heard are good things, but as you say, all shops have staff turnover and things change. That is partly the reason I am looking at the RM/LT hybrid idea. There really doesn't seem to be a reliable source for porting the LT250's (somebody has something bad to say about everyone). And yes I know Q does good work, but he will only setup 2 strokes to run on race gas, at $20+ per US gallon (vs $4.50 for premium pump gas), I am not going to run race gas on my trail bike, so his porting is not an option for me, other wise I would have made arrangements with him for his PWC270 engine when I first discussed it with him back in April/07. For you guys that want to run race gas, you have a viable choice for reliable engine work on your LT's, I am not so sure that anyone in my position does (ie using pump gas).

No Carl, I didn't miss the point. Why would you need a custom pipe for an RM jug when it is essentially nothing more or less than a trail ported 87 LT jug? They share the identical reed cage (I already checked the part #'s), they use the same intake porting, the exhaust port size is virtually identical (differently shaped of course). The only major difference is in the transfer ports. Porting the 87 LT jug's transfer ports to match the RM jug should result in virtually identical performance. Granted the oval shaped unbridged exhaust port will flow slightly better than the stock bridged port on the LT jug (but it is hard to say if the difference would be noticable or not). The big advanatge to the '87 LT jug is that the bridged exhaust port allows for greater lattitude in opening up the exhaust. Obviously there are pro's and con's to both.

If a person could pick up an RM jug on Ebay for cheap (I paid just over $100 for a new OEM 88 LT jug on ebay), put in their choice of piston (I would probably stick with a stock 87 LT250 piston, and buy Q's billet washers (if he would still them to me), given your mixed experience with FTZ), and run the LT pipe of their choice, they would end up with essentially a trail ported '87 LT250, for little more than the cost of a standard top end rebuild instead of, what, $500+ for a descent port job on their '87 cylinder, to end up with god knows what? It seems to me to be a viable alternative, I am not saying everyone should do it, to each their own. It would not require the use of race gas, and provide a substantial increase in HP over a stock LT250.

It's just an opinion, and some information to mull over.

Jim J

Ok, jim, have you had one of the Rm jugs in your hands......
When you do you will notice the angle of the exhaust flange is differnt than on a lt thus Custom pipe being necessary to get the right fit. Also the bolt pattern is a little differnt been a while since I have seen one so dont rember exactly how it is. Last point of differnce I can think of now is the length of the exhaust port. I never measured one but rember the guy at Frozen who I raced against tell me it was longer or shorter....... this being the real reason a custom pipe is needed.

For any one looking for a good trail machine in the 250 motors a 88 + is the one to have..... the larger reed cage of a 86 rm 87 lt reduces intake tract velocity, there by hurting throttle response and low end power...... For a drag app or a big bore above 300cc the larger cage has no noticable draw back and will make more horses power......
Any 250 with the larger cage has potential to make more horse power than the later years, but bottom end will suffer.
Any one who has a motor ported better have the portin done to match the pipe there going to use........... Rules for modification pick the power range most needed, pick the BEST pipe for the application usally motor builders choice then the builder can time the engine to work with the pipe........... if you port the motor and not use builders reccomendation you will buy a lot of pipes trying to find the correct one... Ask me how I know this.......

Carl, unfortunately I don't have to ask how you know, and you are absolutely correct. I would hope that LRD/FTZ/DRI or any other builder, would be willing to discuss the porting options and give an idea of specs (no I don't expect specific details on exact porting) to a "potential" customer, thereby supplying enough info for the knowledable owner to make a reasonable choice in pipe selection.

You are also correct about the power band differences, yes the RM/87LT would be more of a top end motor, but I wonder how much of a shift there would be in the power curve (500/1000/1500rpm?) between the three different cylinders (86RM, 87LT, 88+LT)? I honestly don't know the answer to that question, and unfortunately the only way to know for sure would be back to back dyno runs on the different configurations. Lot's of guys trail ride Banshees and they are certainly not known for their bottom end, but then again, that's one of the reasons I bought an LT instead of a Banshee. I knew the exhaust mounting bolts were turned vs the LT, but was not aware of the different angle, that does complicate things. That's good info to have. which is why I started this thread in the first place.

I haven't decided what I will end up doing with mine, for now it will stay the way it is, stock bore 88LT cylinder/FMF fatty/VF2 reeds/stock carb/K&N filter. Although I am considering a DRI Kiehin PJ36 carb.

Luckily I have lot's of time to mull it over. Thanks for your input.

Jim J

yeah the only thing custom about the exhaust is my exhaust flange...i had to drill 3 new holes. and if you run the rm piston on the lt250 rod you don't have to use thrust washers!!! it eliminates them!!! but you have to use the rm needle bearing to. I just got mine dialed in today. I dropped on jet size and wow...i'll have to get a video of it..she's seems like its running awesome now. and thats on a stock pipe. faster then its ever been with a lt stock jug. but stock vs stock the rm is probably faster. ported vs ported the 87 is gonna be the fastest. It doesn't a 4 stroke low end. but all you gotta do is slip that clutch alittle and bam..all the power is there.

Mike, thanks for the update, saw the video. How would you compare the bottom/mid/top end (RPM wise) to stock? Is there a significant upwards shift in the powerband? Did you put the WSM piston in it, and is it 1 ring or 2?

Jim J

BTW, picked up a complete '86 RM250 topend (cylinder w/powervalve/head/reeds/manifold) from a wrecker just an hour south of me this weekend for $50, still on stock bore, but needs new piston/rings. So now I am really curious to get feedback from guys with the RM top ends.

Mike, I forgot to ask what you are running for gears?

Jim J

right now i'm running i think a 12 and a 42...figured i'd run that because of the 22s. my guy i go to for advice took my quad for a rip and said its still rich. he told me to go two main jets down..lower my needle and drop my piolot jet. so that means its got some more power left in her!
But the power difference. i really couldn't tell you..it didn't ride the quad for several months between having the lt jug and the rm jug. So really i don't know where the difference is because wasn't really used to riding it. i know it feels faster than before.
I am running the wsm piston in it now. i ran the rm for a bit but saw the top of the piston was starting to burn threw ..so i ended up putting the wsm piston i had back it. i hate wiesco pistons..never had any luck with them..even the lt pro lite pistons. but the wsm is basically a stock piston runnign 2 rings..the rm wiesco has 1..but you don't have to use thrust washers.
but you picked one up for 50 bucks..seems like a great buy...but its pretty much a bolt on and go..just gotta turn the exhaust holes a bit..not a big deal..
anymore questions just ask..tomorrow i'll be doing some more jetting

Isn't 12/42 stock gearing? Maybe try a 44 on the back, it'll help rev quicker. I also have 22"'s and went 12/44 to keep the same overall gearing as stock (stock tires were 21's) I am thinking of going back to 12/42 though, with the FMF pipe/VF2's and airbox mods I don't think I needed the 44 tooth rear.

Yes, it was a screamin deal, but there is a bit of a story behind it. I got it from a friend that owns a quad/sled wrecking business about an hour away from me. I went by his place on the weekend (he was cleaning up the quanset where he stores his parts machine) and I saw an RM sitting in the back corner under a bunch of other crap and sure enough it was an 86. Doesn't look like it's ever been opened up, suzuki piston on stock bore. I got the whole topend, manifold/reeds/38mm carb/jug/head. Part of the reason he gave me such a good deal is that I have done lots of business with him in the past and I gave him the left over parts from my wifes Blaster project and some of my left over LT parts (the stuff I would have put on ebay and tried to get a few bucks out of, saved me the hassle and I knew it would help me out some time in the future, so it paid off).

BTW, I think you told me you were running the stock intake, is that the LT or RM manifold, 34mm carb or the 38mm off the RM?

Jim J

hmmm...i your right...lol..i must have changed my gearing on the other quad i had. But i could have swore i went down one tooth on this quad..lol..well i was wrong...
I did some jetting changes today...went to a 230 and still seems alittle fat....runs awesome though..pulls hard...mid and top end are real awesome..i bet its better than before. Could be wrong. really winds out in 6th gear now. never pulled that hard in 6th but now..wow....tomorrow i'll probably drop one more to see how she runs!

I'm running the lt 34mm carb...wish i had a 38mm..wanna sell your for 10 bucks.haha..i think the rm would have some awesome top end with the 38mm carb. i hear you'd lose some bottom end though. i heard if you wanted good low end a 36mm carb is where its at..

but i'm running a lt intake too...it could be a rm465 or something like that too..i think those are all the same..but look at your 86 rm intake..i think it turn to the right...maybe the left..i never had one..but with the 86 rm intake boot you can't use the airbox...

yes, you would lose some bottom end/off idle throttle response. I am thinking of using an 87 LT manifold and a DRI Keihin PJ36 carb, seems like a good compromise. I intend to keep the airbox, where we ride you need one, and the LT manifold will work fine with the DRI carb.

Jim J

yeah...i'm still running the airbox too..i just took my airbox lid off..for now i'm just trying to stay away from water..lol...kinda tough..
yeah...the dri 36mm carb is what i wanted to run...but i'm figuring i'll probably just be selling my quad as soon as i get a few rides in and i know its gonna be reliable..and so far so good!