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

You should be able to see through, and easily. I recently bought a second TTR and had to go through all this again. The carbs are prone to clogging but this could be a function of the bikes being prone to being left in the garage.

I bought one of these

http://www.ebay.co.uk/itm/160973506339?pt

It's just bits of steel rod at known thicknesses. It sounds exactly what the Haynes manuals say not to do but it's not abrasive. You just start with one that will go through and push it through all the holes. Then the next one. When you get to the right size you can feel it and if you try the next size you know you'd have to do damage to get it through, so don't.

That should help but also check the fuel height in the float chamber with the carb off and stood up in a vice if possible. Measuring the float height doesn't seem to work very well. Not for me at least. It's too springy.

Another thing I found on this new TTR was a hunting / hesitation at a steady speed in top (50ish) Couldn't work it out and was about to buy a new inlet stub off Brian even though I couldn't actually find anything definitely wrong with the fitted one. Looking down the throat of the carb I noticed that the needle wasn't quite central down the emulsion tube. I'm sure I've seen that before on bikes and it's not been a problem but I took the throttle plate and linkage out anyway to check the needle height hadn't been messed with. It hadn't but I found the tiniest little thing. I'm not sure if this description is going to work but, the washer with the pin bit in it that locates in the hole and sits between the top spring holder doobry and the needle height clip washer has a little indentation on the underside. It turns out that this holds the needle perpendicular to the throttle plate base when it sits in the gap in the clip washer that holds the needle, thereby ensuring that it goes, near as damn it, right down the middle of the emulsion tube. Upon reassembly, no more hunting or hesitation.

Hope that helps.

Andy

Main jet seems to neck down a little on the inside. Not sure if it should be the same diameter all the way through. The pilot jet I cannot see through but can spray through. I have new jets ordered,  going to replace them because they're cheap enough. Also discovered that the boot has become disconnected from the stub on the engine. Probably not helping.

 

Camoracer34 wrote:

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Carb sat with fuel in it for about a year. Of course the gas went bad and gummed it up. I tore it apart and cleaned it. First start it ran extremely lean. Bike had no power and would cut out above quarter throttle. Tore it down again and did a better job of cleaning it. Jets appear to be clear. Put it back together, bike started right up and idled fine but still cuts out a little before quarter throttle. Again, at part throttle bike runs fine but seems like its not getting enough fuel past part throttle. I held the jet up to light and could see through it. I noticed that it appears to get smaller on the inside. Both openings at the ends are larger than it appears to be in the middle. Clogged or normal? The smaller jet i cannot see through but i can squirt carb cleaner through it. Could this be a jet problem? Need some advice. Thanks!

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 It sounds like another ethanol rooted evil somewhere. Are you seeing steady flow of gas into carb and was petcok rubber in good shape?

Camoracer34 wrote:

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OK. I have checked and double checked the jets. They are clear. The boot came loose from the stub on the engine but I sealed it with high temp silicone and a hose clamp. There is no chance of air getting in there, I even sprayed it with brake cleaner while the bike was idling. Nothing. Bike idles fine and runs smooth until just past part throttle then it falls flat on its face. Acts like its running out of gas. I've cleaned and soaked the carb half a dozen times but still get the same result. Is there anything other than the carb that could cause these symptoms? Dealer wants $400.00 to rebuild it and there is no way I'm going that route!

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Still sounds like carb issues to me. When it was parked last year, was it running fine? If so, bet it's fuel related. I Think you wrote you are getting new jets. Good Idea. If you can afford it, is the best way. While tearing it down, did you notice the float was in good shape and the height set. If bowl level is too low, fuel can't keep up with rev's. and can act like it is running out of gas, because it really is (inside carb., not tank). Did you replace any other parts besides jets? Like plunger and several o-rings that are inside? How many turns out are you?

greg

-- Edited by texasT on Saturday 6th of July 2013 02:36:24 PM

Yes. Bike ran fine without any issues when it was parked. So I'm sure it's due to the gas gumming it up. Only other possibility is that I disturbed something taking it apart. Haven't checked float height yet, been busy, but am planning on doing that tomorrow. I have gasket set with O-rings ordered. Did not order new plunger as the old one seems to be fine. The gasket was the texture of a warm gummy bear possibly due to a 10% ethanol content in the fuel. Waiting on parts and hoping that helps.

OK. Float height appears to be good. Snuck away from the wife and in-laws long enough to put a hose on the bowl drain and check it. Gas level comes up to the top of the bowl. Would anyone advise checking it with the bike running to make sure the fuel level is keeping up with usage? I may try that while waiting on parts to come in.

Camoracer34 wrote:

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Carb sat with fuel in it for about a year. Of course the gas went bad and gummed it up. I tore it apart and cleaned it. First start it ran extremely lean. Bike had no power and would cut out above quarter throttle. Tore it down again and did a better job of cleaning it. Jets appear to be clear. Put it back together, bike started right up and idled fine but still cuts out a little before quarter throttle. Again, at part throttle bike runs fine but seems like its not getting enough fuel past part throttle. I held the jet up to light and could see through it. I noticed that it appears to get smaller on the inside. Both openings at the ends are larger than it appears to be in the middle. Clogged or normal? The smaller jet i cannot see through but i can squirt carb cleaner through it. Could this be a jet problem? Need some advice. Thanks!

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 Bit slow replying, I had the same problem with my TTR - it's one of the valves that operate the acceleration pump possibly the outlet, it drops out when you remove the float bowl - small brass unit, that sits in the float bowl about 6mm dia by say 12mm long. If you spray WD40 into it from both ends it should only work one way (mine was gunked up).

I have cleaned out the carb x3 times but still had this pickup problem, ok at tick but no pickup and needed choke when cooled off a bit - now totally sorted.

You may have cleared it when soaking the carb.

matador wrote:

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Camoracer34 wrote:

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Carb sat with fuel in it for about a year. Of course the gas went bad and gummed it up. I tore it apart and cleaned it. First start it ran extremely lean. Bike had no power and would cut out above quarter throttle. Tore it down again and did a better job of cleaning it. Jets appear to be clear. Put it back together, bike started right up and idled fine but still cuts out a little before quarter throttle. Again, at part throttle bike runs fine but seems like its not getting enough fuel past part throttle. I held the jet up to light and could see through it. I noticed that it appears to get smaller on the inside. Both openings at the ends are larger than it appears to be in the middle. Clogged or normal? The smaller jet i cannot see through but i can squirt carb cleaner through it. Could this be a jet problem? Need some advice. Thanks!

---

 Bit slow replying, I had the same problem with my TTR - it's one of the valves that operate the acceleration pump possibly the outlet, it drops out when you remove the float bowl - small brass unit, that sits in the float bowl about 6mm dia by say 12mm long. If you spray WD40 into it from both ends it should only work one way (mine was gunked up).

I have cleaned out the carb x3 times but still had this pickup problem, ok at tick but no pickup and needed choke when cooled off a bit - now totally sorted.

You may have cleared it when soaking the carb.

---

 The part you refer to is called the one-way check valve...

See here for more info...

http://www.thumpertalk.com/topic/1023378-05-ttr-250-cuts-out-on-throttle/

TT-R250M wrote:

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matador wrote:

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Camoracer34 wrote:

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Carb sat with fuel in it for about a year. Of course the gas went bad and gummed it up. I tore it apart and cleaned it. First start it ran extremely lean. Bike had no power and would cut out above quarter throttle. Tore it down again and did a better job of cleaning it. Jets appear to be clear. Put it back together, bike started right up and idled fine but still cuts out a little before quarter throttle. Again, at part throttle bike runs fine but seems like its not getting enough fuel past part throttle. I held the jet up to light and could see through it. I noticed that it appears to get smaller on the inside. Both openings at the ends are larger than it appears to be in the middle. Clogged or normal? The smaller jet i cannot see through but i can squirt carb cleaner through it. Could this be a jet problem? Need some advice. Thanks!

---

 Bit slow replying, I had the same problem with my TTR - it's one of the valves that operate the acceleration pump possibly the outlet, it drops out when you remove the float bowl - small brass unit, that sits in the float bowl about 6mm dia by say 12mm long. If you spray WD40 into it from both ends it should only work one way (mine was gunked up).

I have cleaned out the carb x3 times but still had this pickup problem, ok at tick but no pickup and needed choke when cooled off a bit - now totally sorted.

You may have cleared it when soaking the carb.

---

 The part you refer to is called the one-way check valve...

See here for more info...

http://www.thumpertalk.com/topic/1023378-05-ttr-250-cuts-out-on-throttle/

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Many thanks, Interesting information, carbs can be fun to sort at times.

I just brought a new strimmer from a well known german company, it claimed to be setup in the factory??? It 4-stroked as I tried to rev it up a bit - being as I am I stripped it down to find one of the tiny valves has stuck down - now it's running ok(shed tuned) I use a 'tiny tach' to setup both saws and bikes

As I said I had the pickup fault on my TTR, early one morning I remembered having an similar fault on my old MK4 Cortina - so I could sort it out.

I had one chainsaw that kept cutting out and running a bit rough - so I stripped down the carb a few times but no improvement, so I changed the ignition module - job sorted.

-- Edited by matador on Tuesday 16th of July 2013 08:00:05 AM