A forum for owners of Yamaha TTR250 trail and enduro bikes!

TTRfan · Super Guru

Carb with slow running problem

TT-R250M · Super Guru

I would suggest before going through all that trouble- buy a new needle set, looks like it's time by looking at that plastic clip. The needle set should be cheap as and worth a try first.

What pilot jet are you running?

AP squirts fine?

Passages all clean including air jets?

Jarrah

Ps. not doubting you Brian, just checking. smile

PlumasDude · Senior Member

I'm curious to see what you figure out. I have a "racing idle" issue at times also. My carb is essentially brand new, except for some gas gunk that I cleaned out. Before clean out the bike wouldn't idle well and seemed lean at idle. After cleaning the lean problem went away but my new symptoms are popping when backing off throttle and a sometimes racing idle.

My idle symptoms are that it sometimes wants to idle at about twice normal speed, but just sometimes, especially when good and warm while riding. I really noticed this because your (Brian's) bashplate won't let the brake lever travel too far which caused me to discover my rear brake line was mushy and needed bleeding. I discovered this on a long steep slushy downhill single track -- you really notice the racing idle when you're relying on engine braking in first or second gear. I've now fixed the brake but still get the idle issue at times. I find that if I come to a stop with the racing idle and work the throttle a few times idle will eventually go back down to normal.

Its an intermittent issue, I can't tell what triggers it (but I haven't spent too much time testing it and haven't taken the carb back off to see if I screwed something up -- which is usually the explanation). Setting idle speed as low as possible seems to help, at least it makes it easier to "work" the throttle back to normal idle.

But come to think of it I'm not entirely sure the idle issue wasn't there all along, even before the carb clean. Still using the 50/137 jets.

So Brian are you saying that the throttle linkage above the needle is sticking or something, causing the throttle to stay somewhat open even if you think you're throttled down? Jarrah I don't quite understand how a worn clip would give this sort of intermittent problem, are you saying maybe there is leakage around the clip, or maybe the clip is moving?

I try to remember: (1) its just a TTR, not so high tech; and (2) (as my son keep saying) why are you idling?

Markvan · Guru

My carb seems similar to Brians and plumas. Only 9000 kms on the clock with very little dirt work. Air filter clean. The idle is a tad slow and if i screw idle up it revs a tad to high. Its like 600 rpm is to slow and the next rev i can obtain is around 1000 rpm. I cant seem to get a rev of 800 rpm. Ive played with the mixture screw with no difference. Maybe i am being abit fussy with my idle revs. But it doesnt seem all that consitant with revs being where they want from 600 to 1000 rpm. To me 600 rpm seems to be close to stall. 1000 rpm seems to rev abit high to use engine braking. My rev calculating are all an approx Guess.

PlumasDude · Senior Member

Sounds like mine. Except my "idle racing" speed is probably more like 2000. I checked my not-so-helpful manual and it recommends an idle speed of 1250-1350 (!), so maybe this set up just won't idle at what I'd consider normal. But if I set it at over 1000 rpms the racing issue seems to happen more.

TTRfan · Super Guru

Thanks for suggestions and feedback guys biggrin

Interesting to hear that two TTRs with low mileage carbs are having the same issue.

The carb I am having idling problems with has some miles behind it which probably explains the worn bracket. My theory is that this free play allows the slide to flutter when the throttle is closed hence not having a reliable idling speed.

My brother-in-law's TTR is suffering the same symptoms and we slightly improved things by raising the needle one rung which surprised me as my understanding is that only the pilot jet is used on low or closed throttle. Haven't checked his linkage bracket yet....

However, I doubt your (PlumasDude and Markvan) carbs will have such wear so maybe we should be looking for something else. Not sure what though confuse

I have replaced the pilot jet with a new standard jet and no difference. I have checked the airways and put the carb through an ultrasonic cleaner a couple of times.

Just to emphasise the problem is solely at idle with a fully closed throttle.

I think I will stick with my plan to change the linkage and see if that solves the problem.

Brian

TT-R250M · Super Guru

PlumasDude wrote:
Jarrah I don't quite understand how a worn clip would give this sort of intermittent problem, are you saying maybe there is leakage around the clip, or maybe the clip is moving?

I am not saying that the worn clip would do that, I am saying that from the state of the plastic clip, the needle set needs replacing.

List of things to check-

No loose screws or jets inside carb.

Throttle cable for wear and proper adjustment (free play).

Carb slide cut-out is at the rear of the carb (airbox side)-

The return spring can go two ways, make sure it is the right way as pictured below-

Air jets-

More info here- http://ttr250.activeboard.com/t55374798/rebuilding-a-ttr250-teikei-y30p-carburettor/

Jarrah

PlumasDude · Senior Member

Great detail, much better than the manual. I relied on the stickies last time around, thanks!

TT-R250M · Super Guru

Just thought I would add that anyone that cannot sort the carb out and is willing to pay postage to Australia and the return, I would be happy to give it a once over to check everything (or clean) and send it back free of charge.

Jarrah