You might be on the right track. I would suspect a bad or incorrect needle and seat assembly. I used a couple from aftermarket rebuild kits and the opening is too narrow. They don't allow enough fuel to enter the bowl when you run wide open throttle for long periods of time. The float should be adjusted at or around 25/32nd. Too much more than that, than it will leak out of the overflow. Dr ATV's (Beatrice) sell a needle and seat assembly with the largest orifice I've seen. Plenty of fuel flow.
Additionally, verify your gas cap isn't defective by riding your bike with the cap off and see if the bikes performance improves. If it does, than the gas cap is the culprit.