your float is probably stuck. if the bike sat for a length of time, you may need to clean out the carb. its not that hard,but you'll need a carb rebuild kit. gaskets need to be replaced, and maybe the jet needle. should all be in the kit.
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Stuck float?
Float may be stuck in carburetor, or you may need to turn the petcock to the off position when not riding (if applicable). ~RC@HD~ ANSWER: Another posibility is that the gas cap is not venting correctly and when the bike sits in the sun, presure builds up in the tank forcing gas out of the overflow vent in the carb.
Typically this is caused by a dirty carburetor causing gas to leak through and into the crankcase.
your float is stuck in the carburetor. Clean it with carb cleaner.
Dirty or stuck open needle valve in carburetor.
Seals, or float level.
The float valve in the carburetor is not working properly. You will need to remove the carburetor and clean it or replace it.
Your carburetor is loading up. Or your needle valve is out of place or stuck.
1. drive it until you are out of fuel. it will quit leaking. 2. rebuild the carburetor. 3. replace the carburetor 4. identify the reason that it is leaking and then ask another question.
If it's coming out the overflow pipe, then it's likely to be a sticking float.
Three possibilities: The carburetor is set to run too rich, the plug is fouled and is not get sufficient spark, or there is a leak. Start with the leak and work backward: leak, spark, carb.
Most likely, Your float is stuck in the carburetor. If it is stuck open gas will continue to flow into the carburetor bowl, then it will flow into the crank case and cause your oil level to rise. You need to take off your carburetor and adjust the float.