Mikuni TM carb trouble

[rlb478]

I have a 1991 RM 250 which has been rebuilt completely, new crank bearings, seals, piston and rings, rod bearings. The reason for this was a very high idle as if it was an air leak. I have determined it is the carb after all this, what I am curious about is the center inside section of the carb pulls out and upon doing so I have found a torn O-ring, since it is not directly in contact with outside air could this still be my problem. I know for sure it is the carb, I took the Kehein off my son's 1995 RM250 and it runs great. I'm just trying to figure out what part of the carb is malfunctioning to cause this problem.
Thanks,
Randy Bane

 

[2strokes4life]

I am curious to hear what the possible solutions are. I too have a 1991 RM 250 that I have rebuilt. Mine idles high at start up and then does settle down a bit after it runs. I've been working on jetting, but can't seem to get it right. I changed both crank seals thinking I had an air leak. I changed all the internals that I thought I could by looking at the parts fiche. I soaked the carb in carb cleaner overnight. I wonder if I damaged rubber parts that aren't on the parts list that you can't see. I do have gas coming out of the overflow and have adjusted the float height about a dozen times. Maybe I did it wrong, but I did replace the seat and float valve assembly. I did just read also that it is possible to have the float in upside down. Who knows. Let's see what the experts have to say about your high idle. Maybe a new carb is in order for me.

 

[rlb478]

Today I purchased a used TM carb , put it on the bike, runs great! Don't know what exactly was causing the problem with the original carb but my bike lives again, ready to head back down to Haspin!

 

[2strokes4life]

If you don't mind me asking, where did you find the carb and how much was it. Would it be possible to put a new TM carb on this bike. I mean would the new carbs fit a 1991 Suzuki RM 250? I've thought about a new carb. I'm afraid if I buy a used carb, I might just get another piece of garbage. The thing I don't understand is I have totally rebuilt the carb except for the slide and the carb outer casting (body).

 

[rlb478]

I got mine at a place in Indianapolis called Two Wheels Enterprises and he only charged me $45.00 it was pretty dirty, but after cleaning, worked great. Dennis Kirk has the new TM carbs for $169.00. I know how you feel about cleaning everything, I did the same. The only thing I can think of is there is a hairline crack in the housing allowing to much air in after the carb slide, thereby causing the incredibly high rpm at idle.

 

[truckster225]

Lots of things could be wrong with the carb. EVERY O ring is important(or it wouldn't be there). Also, that carb is nearly twenty years old! There could be dried seals, the top cap could be cracked. Even the gap between the slide and the wall could have worn itself bigger! If you've got a new carb and its working for ya, I would just scrap the old one. Its a damm shame you had to go through SO MUCH trouble to find out it was the carb!

Was all that work done in a shop?

 

[rlb478]

No, I did all the work myself, been tearing apart 2 and 4 cycle engines for almost 30 years, when something wasn't working right had to see what the problem was!

 

[truckster225]

Hey, well maybe you can help me out! Ive redone lots of 2-strokes, but know im on my FIRST 4-stroke. Im totally self taught, trial and error. Im pretty confident, but I just have a question, The cam chain! Whats the best way to go about handling that when all I want to do is remove the head??

 

[mathd]

i like to hear about 4 stroke too.
first engine i did was a 1985 suzuki 250lt quad engine(4 stroke).
Am pretty sure the quick way the oldschool guy showed me back then is not the same that other people use to do it lol.