Tip & How-To about Motorcycles

Float valve overflowing on a motorcycle

My Yamaha wr250 was leaking fuel out of the overflow badly. I cleaned the seat, changed the valved, adjusted the level. Nothing worked. In the end, it turned out the seat was damaged due to age. Yamaha did not sell a new seat for it, you have to buy a new carburetor. Here is a tip that is easy to do to resolve it provided you have already replaced the float valve, adjusted the float level, and cleaned the carb.

Items needed:
a small tube of lapping (valvegrinding) compound(Available at your local auto store)
1 can carburetor cleaning fluid.
About 5 Q-tips (If your float valve seat hole is bigger than a normal Qtip, you can purchase oversize ones at any drug store)
High speed drill

remove the carburetor, bottom bowl, float, and valve.
Put one Q-tip at a time in the drill
Apply a dab of lapping compound to the end of the tip(about twice the size of a b.b.
Stick it in the float valve seat and letter rip for about 10 seconds. The Q-tip will take on the shape of the float seat and lightly polish the seat smooth again. You might want to do this a couple of times the first time to ensure it takes.
Once you are satisfied that all scars are removed, take a can of carburetor fluid and spray out the seat. Ensure that all the lapping compound has been removed.
Put the carb back on. Try out the bike and see if you can get it to leak. If it does, repeat the process. I had to do it about 5 times to get mine to completely stop.
Final Note. This tip is provided for people that have already replaced the float valve, adjusted the float level, and cleaned the carb. If you cannot purchase another seat for your carburetor, without buying a new carb. this beats that hands down, but I strongly suggest you do the first three steps first. Anything goes wrong, your not out anything anyway.
Ride hard, or stay home.

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1 Answer

When I try to accelerate the engine stalls on my Yamaha wr250

Hi, Chathuranga and the usual suspects are:
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No. Wrongly adjusted float height makes the engine fail to run.
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That is because the over flow holes on a carburetor are so far above the floaters that even with the float height wrongly adjusted, the fuel needle should stop the gas from overflowing and simply made your fuel mixture too rich.

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Hi Jwelden,
Have you checked the float level in the float chamber?
I guess you may have to reset the float pin adjustment, its allowing more gas to pass through thn required and thus the overflow!
Not bad too, when you are working on the float assembly take the opportunity to blow out the fuel line from petcock to the carburator via the seat for the float pin,any foreign particals there would stop the float pin to seal up and thus overflow.
Fit in an inline fuel filter , this will help keep out the dirt or whatever.
Hope this helps.

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Feb 13, 2009 | 2003 Yamaha WR 250 F

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