Motorcycle Repair: fuel leak, float bowl, petcock

Question
Chris --- I have a 1980 Yamaha 650 special II. It leaks gas through the air filter on one carb only. this is only after it is shut down. Does NOT leak when running. The fuel cock does not shut off the fuel completly when in the on/off position. I have checked the floats and sprayed carb. clean but no help. What do you advise?
Thanks
Joe

Answer
Hi Joe.
 The answer here is obvious.  There are 2 definite things wrong here.

1)  You have a leak in the float bowl.  It is related directly to either the float or the seal that allows fuel into the float bowl.  The float could be bad.  Is it the original?  Replace them on both carbs.  Check the seals.  Perhaps they need replacing.  Perhaps the float itself is sticking open.

2)  The petcock is allowing fuel to flow when in the off position.  Either rebuild it with a rebuild kit or replace it with a new petcock assembly.

 The carb does not leak when running because the engine is using the fuel at the same (or faster) rate that it is leaking, so it won't overfill the carb while the engine is on.

Remember that all systems on the bike function in a logical process.  Learn the process and the problems get smaller and easier to fix.

Let me know what you find.
Good luck.
FALCON