So I just bought a 2009 yz250f from one of my friends, its got a new motor in it (bottom up) and has been running great! About a week ago we were out trail riding and started back firing and popping mainly on decel and wouldn't idle.. I had just bought gas from a different station that morning in a hurry and figured maybe it was bad gas so I pulled the carb apart and cleaned it out. Now it will idle and isn't back firing nearly as much but seems like it is kind of missing thru about 1/4 throttle and then cleans up? It's also been dumping a little gas when i put in the back of my truck.. Could the float level be causing this?? From about 1/4 throttle on it runs fine.. Any help is greatly appreciated!!

1/4 throttle and below is pilot jet circuit. Idle is mixture screw adjustment. Make sure the idle mixture screw is adjusted properly and that will determine if your pilot jet is too rich or too lean. If gas leaks out when the bike leans then that is normal but if it leaks when the bike is straight up then yes the float needs adjustment.

Thanks! I ended up getting it tuned right with the mixture screw and a new spark plug which I'm guessing was toast from the bad gas? Took it out and trail rode and hit the motocross track this weekend and it's running great! Thanks again!