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:
1. Idle circuit and transfer ports clogged.
2. Air fuel mixture adjustment too lean.
3. Pilot jet clogged.
4. Faulty accelerator pump.
5. Float level too low.
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10. The gas cap is not venting properly or fuel tank venting system blocked.
11. Vacuum line from intake manifold to petcock broken, cracked, or not attached, carburetor vent line plugged.
12. Needle and seat stuck closed in the float bowl.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have nice a day.
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Hi, Anonymous and the usual suspects are:
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No. Wrongly adjusted float height makes the engine fail to run.
If you get over flow leak (from the overflow hose) your fuel needle inside the carburetor simply does not close the gas supply hole firmly even if the floaters still pressing it against that hole.
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, Michael and the usual suspects are:
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5. Worn or dirty inlet valve or seat.
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1 Answer

2003 WR250 F - eng. won't idle down and carb starts to overflow


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.

Knight (Yamaha Seca XJ750A 1981)


Feb 13, 2009 | 2003 Yamaha WR 250 F

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