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Carb with slow running problem
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I have a carb that checked over fine. All jets cleaned or replaced, etc.

However, there was an idle problem where on occasions the engine would run at a fast tickover and other times it would be OK.

I know there is another post about these symptoms somewhere but darned if I can find it confuse

I took my own advice and checked the link mechanism (or bracket as Yamaha call it) just above the slide and found that there was quite a bit of play in the black joining piece joints as indicated by the green arrows in the pic below. 

To the right of my worn bracket in the first pic is one from another TTR which has an all-metal bracket and has no play at all.

The bracket is available new but is over £100 no

For the time being I will swap out the bracket but I will be left with an incomplete carb so I guess I am going to have to look at making up a new version of the black section. 

I will let you know if that solves my idling problem. Can't think what else might cause it confuse

Slide mechanism 1.jpg

Slide mechanism 2.jpg



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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



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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?

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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. 



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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.

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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

 



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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-

553027_562393563794119_1622177328_n.jpg

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

Jarrah



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

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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



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You the man Jarrah thanks for the offer! I'll fool with the needle first when I can find time.

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PlumasDude wrote:

You the man Jarrah thanks for the offer! I'll fool with the needle first when I can find time.


 No dramas, let me know if you get stuck.

Jarrah



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RE: Carb with slow running problem - PROBLEM SOLVED!
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After stripping the carb for what seems a zillion times, I am pretty sure I found the cause of the erratic idle biggrin

After fitting a new diaphragm, seals and jets, ultrasonically cleaning the carb a few times, blowing out all the airways, etc, and not remedying the problem, I spotted a tiny amount of play in the linkage this morning.

Carb link1.jpg

 

I peened over the collar - well, actually, I cheated and squeezed it up in the vice, refitted everything and took the TTR for a test run. Ticking over perfectly. The occasional fast idle seems to have gone biggrinbiggrinbiggrin

Carb link2.jpg

 

I hope that may help any other owner with the same issue.

Brian



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Super Guru

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RE: Carb with slow running problem
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TTRfan wrote:

I have a carb that checked over fine. All jets cleaned or replaced, etc.

However, there was an idle problem where on occasions the engine would run at a fast tickover and other times it would be OK.

I know there is another post about these symptoms somewhere but darned if I can find it confuse

I took my own advice and checked the link mechanism (or bracket as Yamaha call it) just above the slide and found that there was quite a bit of play in the black joining piece joints as indicated by the green arrows in the pic below. 

To the right of my worn bracket in the first pic is one from another TTR which has an all-metal bracket and has no play at all.

The bracket is available new but is over £100 no

For the time being I will swap out the bracket but I will be left with an incomplete carb so I guess I am going to have to look at making up a new version of the black section. 

I will let you know if that solves my idling problem. Can't think what else might cause it confuse

Slide mechanism 1.jpg

Slide mechanism 2.jpg


I had another look at this particular carb this morning and found an obvious problem that maybe I should have spotted before disbelief 

Slide mechanism 1.jpg

I am not owning up to have caused the problem but the spring indicated by the purple arrow should have been inside the hollow black plastic joiner and, when properly located, it takes up the slack! I have put the carb back together and it's now working perfectly biggrin

Brian

 



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