Float height set to high, needle and seat stuck, bad reeds, elecric issues.. there is a few things it could be. First thing I'd start with is pulling spark plug boots of, cut wire back half inch, spray both ends of boots out (carb clean, brake clean, electrical contact cleaner). Then move to checking float height and needle and seat.. pull reeds make sure they are not chipped or cracked, and they are closing all the way. Also check jetting may be just to rich.. jmo