mikuni tm38 tuning trouble

hey guys, i have a '94 xr650l with a mikuni tm38 carb and i've been having some trouble getting it running right. for the most part it runs decent although a little rich. the problem is after the bike is warmed up it likes to stall at idle at stop lights and such. it idles fine when i first start it but it seems to stall when i slow down from a higher speed. its has the mikuni carb, uni air filter, and supertrapp exhaust. also it seems to be down on power but i don't have a way to prove that. do any of you guys have experience with that carb and/or tuning information for it? i cant seem to find anything concrete for it. thanks!

Is the carb clean? Sometimes sediment can settle and allow a good running bike while cold but after getting agitated by running, it will start to cause issues.

A 38 is kinda smallish for a 650. Might be the "down on power" issue. Check for a possible bent needle as to the erratic idle. I just did an L with a TM41 and the idle problem was mostly due to the needle and a bit to cable routing. TMs always seem a bit rich and performance will suffer if they are too much so.

Edited by valvesrule

Honestly I'm not sure if it's clean. I was trying to see if there was any point in keeping the carb or just upgrading

10-4, it is a bit on the small side but I would think you should at least be able to get it to run well even if it is holding the top end back.

Honestly I'm not sure if it's clean. I was trying to see if there was any point in keeping the carb or just upgrading

I have a 38, 40 and 41 here. They all seem to have an idle issue as you describe. I suspect the pilots are just a smidge to big so they load up after a quick sprint going into an idle. I have a 40 Dellorto pumper on my L and it never gives me the idle issue the TMs have. If you decide to dump the carb give me a PM. I can always find a use for one. Edited by valvesrule

Okay I'll keep that in mind. I could take it apart and clean it but it still feels like it's underpowered. If I upgrade would I be able to use the throttle cables I have and just switch the carb?

If I upgrade would I be able to use the throttle cables I have and just switch the carb?

The TMs can all use the same throttle cable.

What about upgrading to a 40mm fcr? Would the cables work for that?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now