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Yam XT550, carb problem. Fuel leak, but all parts move and look perfect.

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Hi all

I’m working on an ’83 XT550.

The carb is leaking fuel. Some facts:

1. The floats are fine, they are not leaking. They float if put in gas.

2. The float height is according to spec.

3. The carb needle looks perfect.

4. The valve seat looks perfect.

5. The valve is 100% tight if I tilt the carb to let gravity help the float push on the needle.

However if I put the carb in the bike (or hold it vertical) one of the following happens:

1. The carb does not leak fuel

2. Some fuel drips from the overflow.

3. Fuel gushes from the overflow AND the breather tube, meaning the carb us FULL of fuel

4. If I tap the carb with a screwdriver the carb stops leaking fuel..

SO – the valve or float somehow get stuck and let fuel by, until I tap the carb, then the needle valve closes and the leakage stops.

I have had the carb apart maybe 20 times, but can’t spot how the needle or floats get stuck. Everything moves smoothly and there is no snagging.

Any ideas???

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I had a carb that I could not figure out, I too had taken it apart many times and putting in and taking out the carb on this bike(83 XT250) is not one of my favorite tasks! I was fortunate to find a replacement carb and a rebuild kit and now the bike runs great! The way I look at it with getting a replacement carb was at least I'll have the old carb for parts! Sorry I could not help diagnose your carb issues, maybe someone with a little more knowledge then I will chime in. Good luck!

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I had a real good experence with a company called Sudco Mukuni, when I bought a replacement carb for my tt500, it was reasonably priced, and it came jetted to the requirments of the bike, they ask things like what pipe you run, etc. Good luck... phillybeef......

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xt550 has two carbs--yes? ck the bowl gasket--make sure it isn't rubbing float when you put the bowl on.

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Thanks guys.

I managed to fix the leak by polishing the float valve seat with some fine stranded steel wool. I’m not 100% convinced the problem has gone away completely (the carb leakage was sporadic) but the problem is certainly less than before. The seat appeared sparkly clean but somehow the polishing helped.

I guess I will buy a new valve if the leakage comes back.

Bergman501, yes, two carbs. Funny you should mention the gasket, it was the first thing I checked today…

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It's two carbs, but only one bowl. And the biggest Pain in the butt single cylinder carb to take out. Only my street bike is worse and that's an inline four!

If I were you, I'd install an in-line fuel filter. You could have crap from the tank holding the valve open causing the leak. The nice thing is you won't have to take the carb apart to install it.

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It's two carbs, but only one bowl. And the biggest Pain in the butt single cylinder carb to take out. Only my street bike is worse and that's an inline four!

If I were you, I'd install an in-line fuel filter. You could have crap from the tank holding the valve open causing the leak. The nice thing is you won't have to take the carb apart to install it.

Yes, the carb is a pain to get out. But I have been getting a lot of practice in the last few days, it gets easier ...:-)

Good tip regarding the inline filter. Already have one....

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