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

Jeff · Newbie

Carb. Idle Problems

TTRfan · Super Guru

Hi Jeff and welcome to the forum

It sounds more like the inlet stub is leaking than a carb problem.

The rubber can split (rare) or, more commonly, the rubber parts from the metal stub as in the pic below. This can allow air in and not always be obvious.

Brian

carb stub apart.jpg

Jeff · Newbie

Update. The issue turned out to be the Carb slide linkage slop (play), which has been described here in the past. I re-swedged the arm to the shaft and re-swedged the broze connecting link. Runs absolutly perfect now!!! You can test for this play by removing the carb and place you index fingers in each end grabbing the slide and moving it up and down, checking for free play.

Patrik · Member

Help - my TTR stays on high revs!!!!!!

TT-R250M · Super Guru

Help ttr stays on high revs!!!!!!

Patrik · Member

hi there thanks for the response it sticks at high revs

Patrik · Member

thanks for your response - the problem is that the engine revs do not go back idle when the throttle is backed off to rest - when the bike is running you can rev it up a bit and let the throttle go but the engine will rev like the throttle is stuck on - the throttle cable has some slack and the throttle actuator on the side of the carby goes back to the idle adjustment screw stop as it should but the engine still revs high - if you blip the throttle a bit it will eventually go to proper idle or sometimes stall. It seems as if something inside the carby is sticking or that the slide is sticking up a bit but that doesn't seem possible - we have taken it apart a bit and cleaned out the jets etc but that hasn't made any difference. We've also cleaned out the choke starter thingy.

I'm scratching my head - checked all the obvious things but they all seem ok.

Any more suggestions?

Thanks.

petenz · Super Guru

I have seen a bent needle slow the return of the slide.
It was a very small bend...

Patrik · Member

Help - my TTR stays on high revs!!!!!!

TT-R250M · Super Guru

RE: Help ttr stays on high revs!!!!!!

Patrik · Member

the problem was the screw that locks the slide lifting mechanism to the shaft that is turned by the throttle cable was a little loose - this allowed the slide or throttle valve to not close properly. Easily missed - now bike runs fine. Only had to take the carby off 3 times to find it. Feels good now though. Thanks for all who tried to help. Much appreciated.

Ciao.

TT-R250M · Super Guru

Patrik wrote:
the problem was the screw that locks the slide lifting mechanism to the shaft that is turned by the throttle cable was a little loose - this allowed the slide or throttle valve to not close properly. Easily missed - now bike runs fine. Only had to take the carby off 3 times to find it. Feels good now though. Thanks for all who tried to help. Much appreciated.

Ciao.

Oh, you mean this one...

Inside top of carb.jpg

In that case it wouldn't hurt to check the tension of the two slide retaining screws...

Thanks for the update, oh... Welcome to the forum

Jarrah

ttr_paul · Member

Engine revving on its own, wont return completley after revving

Cubber · Super Guru

To me it sounds more likely to be a kink or snag in a throttle cable - or lack of cable lubrication. confuse

Also - check the quadrant on the top of the carburettor and play in the cables.

Martyn

ttr_paul · Member

Hi Martyn, cables are routed correcdtly and throttle returns very well when the engine is not running. Also lubed ok.

Cubber · Super Guru

It's not the cables then. disbelief

I always start at the easy end of a problem - ever since my Bandit wouldn't start after I switched it off. It took me an hour and a half to work out why. confuse confuse

I'd switched it off using the kill button and never re-set it!

Time to start looking at the levers and linkages then, before removing the carburettor to tearing its innards out. bleh

Martyn

Bsturkie · Member

TTR_Paul,

I would disconnect the cables from the throttle linkage. You probably will need to remove the gas tank. That's pretty simple. Once cables are removed, replace gas tank and crank and let idle. Manually move the linkage cam throttle arm. If the slide doesn't snap back then you know where your problem is. I had the same issue in the thread under this one. Good luck.

Brandon

ttr_paul · Member

Hi Brandon, this one isn't hesitant, its the opposite. If you rev the bike at a certain RPM then it carrys on revving by itself!

peteBLUEttr · Super Guru

It definitely isn't drawing extra air in through anywhere then?

ttr_paul · Member

I don't think it is, did also try spraying the inlet area with brake cleaner and no signs of increase in revs

TTRfan · Super Guru

Fladdem had a similar issue and I have come across it before. Screw loose in the top of the carb allowing the throttle arm to slide linkage to move. See here

Also see here

ttr_paul · Member

Hi Brian, can't find any loose screws. Had a look at your thread but ended up very confused. It seems to say that the issue was a metal collar that had play in it and needed to be squashed to stop the play, but then underneath it says the problem was a spring that was in the wrong place?

Watts · Member

I have the same problem as well as the original post. I think my needle set #6 on this parts diagram is sticking, but am interested in what part#38, the diaphragm, does same diagram?

I think it's for the accelerator pump, but if it's associated with high, sticky idle with no throttle I should replace/fix it as well? I have been through a lot of other diagnostic tests, also interested in the post here about the sticky linkage as I can't rule that out when we all run the same stuff. That is easy fix, crimp it tight. Frustrating and common problem for sure: guess we'll all get good at taking out the carb.

leigh · Senior Member

Love some more clarification on this as mine is doing EXACTLY the same thing as yours ttr paul.

Only when running. I think it may have been there for a little while but I have only just properly noticed it.

TTRfan · Super Guru

Watts wrote:
I have the same problem as well as the original post. I think my needle set #6 on this parts diagram is sticking, but am interested in what part#38, the diaphragm, does same diagram?
I think it's for the accelerator pump, but if it's associated with high, sticky idle with no throttle I should replace/fix it as well? I have been through a lot of other diagnostic tests, also interested in the post here about the sticky linkage as I can't rule that out when we all run the same stuff. That is easy fix, crimp it tight. Frustrating and common problem for sure: guess we'll all get good at taking out the carb.

The diaphragm is the main part of the accelerator pump. See here for more info.

To test it is working, make sure there is fuel in the float bowl and then open the throttle. You should get a squirt of petrol from the short brass tube (at the bottom of the airbox side of the carb) toward the throttle slide.

Brian

leigh · Senior Member

So to clarify, and copy Pauls comment

"started to carrying on revving when you rev it and if I look at the throttle cable wheel then it sits just off of the fully returned position. It doesnt do it with the engine off,"

Mine does the same thing, it you let the throttle snap back it doesn't do it. But it you let it go back not so rough it will sit a mm or 2 off the throttle stop. But only when running.

So causes could be loose screw in carb, play in the arm/linkage due to wear? I've recently replaced all the seals and new jets etc. Been running perfectly.

I have on the odd occasion out riding thought that it was me not backing off the throttle correctly and getting the odd heart attack moment as the bike wanted to keep going. Throttle cables and throttle are all well lubed.

I'll re-do those though and pull the carb and check all the screws etc. I'm not sure I'm confident pulling out the whole linkage arm etc. My bike has done 16500klm so a bit of wear could be the reason.

Brian you suggest peening over that washer to remove play in the linkage, and also ensuring correct fitment of that spring that takes up tension in that area. Anything else anyone recommends I check? I have not replaced the slide and needle set. Could they be worn causing this?

Reason for all the questions is so I hopefully don't have to pull and strip the carb 10 times :)

Any help appreciated.

Cheers Leigh.

leigh · Senior Member

Ok installed the new slide. Problem solved.

Much smoother carb operation now. Also cleaned the carb barrel etc and residue the exact same colour as the slide came off the barrel. The new slide was much smoother to touch etc than the old one. Comparing the two quite a bit of coating had come off the old one.

Absolutely nothing else was wrong with the carb, nothing loose, no excess play in anything, all working parts/seals replaced over the last few months (to my limited knowledge). This solved the revving up issue for me. Throttle action is much smoother now, I've always kept the cables and throttle tube well maintained and lubed etc.

Wonder if its just general wear or if carb cleaner compounded the problem? I suspect just wear but my bike has only done 17,000klm.

I can now take the carb out of my bike blindfolded with one hand behind my back :)

Leigh

jasparach · Senior Member

Hi Leigh, thats good to know that the new slide cured the sticky throttle for you,
i got mine to work some way reasonable by getting rid of any free play in the cables
but it still is not perfect, i can ride it but need to be careful once the throttle twists to
a certain point it can get sticky and i need to twist it back manually. I think a new slide
may be on the cards for me if i can get it for a reasonable price.

John

leigh · Senior Member

Just to follow up on this, done quite a few klms now with the new slide. It has definitely fixed the problem. Plus a much smoother throttle action now.

nelly · Senior Member

94 raid sticking throttle

peteBLUEttr · Super Guru

Slide/needle wear

nelly · Senior Member

thanks buddy,
is that a deffo?

I have a feeling you are talking from experience lol

peteBLUEttr · Super Guru

That's my thinking anyway, if it is notchy from applying power directly on the actuator then it obviously an internal part/parts.

nelly · Senior Member

thanks mate
"actuator" I like that, its better than thingymebob ,
cheers

peteBLUEttr · Super Guru

Throttle actuator I call it anyway...

jasparach · Senior Member

Yes it's the slide in the carb that causes it, works fine when the bike is not running
but when it is running it sticks. It happened mine as well as a few others, Leigh on here
fitted a new slide to his and it transformed the bike he said but they aint cheap to buy.
I got mine to run some way reasonable by removing any free play from the cables when they
are connected but it is still not right, usable but not right.

ttr250.activeboard.com/t59996391/engine-revving-on-its-own-wont-return-completley-after-revvi/

nelly · Senior Member

cheers guys,
well ive had the carb off, and by the look of it its been off before [ no surprise there ] I noticed plenty of scratches from screwdrivers etc, around the screws on top of the slide,and it looks like the PO used a driver to re-install the carb into the rubbers, anyway I dropped the needle by raising the clip from 3rd from top to 2nd from top, whilst taking it apart I found a spring rattling around inside,NOT the one around the plastic clip at the top of the needle ,but it was 12-15mm in length and half the diameter, about the size of the spring in a biro ,ive looked at several diagrams of the carb and I cant see it ,or where it could be,

so I re-fitted the carb, and ran it round the block half a dozen times ,and guess what??

................................... it now seems fine , I can only guess that it had been bodged with a biro spring for some reason hmm

if that spring is supposed to be there somewhere I'm sure one of you lot will tell me where,

jasparach · Senior Member

That was a handy fix,if only that was the case every time we'd be away for slates!

peteBLUEttr · Super Guru

Good outcome.

TTRfan · Super Guru

nelly wrote:
whilst taking it apart I found a spring rattling around inside,NOT the one around the plastic clip at the top of the needle ,but it was 12-15mm in length and half the diameter, about the size of the spring in a biro ,ive looked at several diagrams of the carb and I cant see it ,or where it could be,

so I re-fitted the carb, and ran it round the block half a dozen times ,and guess what??

................................... it now seems fine , I can only guess that it had been bodged with a biro spring for some reason
if that spring is supposed to be there somewhere I'm sure one of you lot will tell me where,

I may have missed one (or two) but I reckon there are 6 springs in or on the carb that might meet your description as shown by blue arrows on the diagram below.

Some float bowl drain screws on later TTRs were fitted with a spring which isn't shown on the fiche - but I have added an arrow for it anyway wink

Brian

carb springs.jpg

nelly · Senior Member

thanks brian [ yet again ]
you are the man

that's a really good diagram,havent seen that one, HOWEVER............#37 at the top, looks like the culprit , I deffo didn't fit that one,and I didn't disturb any other part of the carb ,I only took the top off to get to the slider, if it keeps running as it is il leave it until he gets his fmf that he wants, then i will re-fit it when I sort out the jetting, good job I didn't bin it, he only rides it up the lane and back once a week ,hes not passed his test yet ,so if it goes wrong it wont leave him stranded too far away,

thanks again bud
nel

TTRfan · Super Guru

Pleased to have been able to help!

#37 is the return spring for the diaphragm actuator arm (now where I have I heard that description before biggrin ) - part of the accelerator pump mechanism. The diaphragm has its own spring (also #37) as shown toward the bottom of the diagram so nothing much to worry about as you rightly surmise wink

Brian

nelly · Senior Member

thankyou

and sorry P.O ....................... my bad biggrin

saintken · Veteran Member

Just going back to the sticking throttle slide theory, in the past I've had this problem only when the engine was warm. Turned out that the slide had gone very slightly oval, which couldn't be seen but could be measured, as the carb got slightly warm the expansion of the slide and body caused them to touch and stick! Short term solution was to polish slide to reduce high spot long term solution was a new slide.

nelly · Senior Member

yeah if it does start acting up,a new slide will be on the cards,
but have you tried to get ANY money off a 21year old . if I know him he,ll wait until I cant put up with it any longer and paid for it myself.
he don't know it yet but when my ttr arrives early next week,his will be on the back burner lol
thanks

Benjah · Veteran Member

RE: Help - my TTR stays on high revs!!!!!!

Dylan Macdonald · Newbie

Hi I know the problem! I have the same bike and had the same problem if you open the carb there's a arm that moves the slide up and down and there's a bolt 🔩 that joins the outer arm and slide together that bold likes to strip and come loose and causes the slide to get stuck up and get caught on the arm I promise you that's the problem I was dealing with the same thing using the bike everyday and it killed me when I sorted it out it was like a new bike I swear

Good luck

ttr steve · Super Guru

Good work and thanks for sharing, I have never heard of that before.