As dan mentioned, check your float heights first. I know this caused the same issue for me a couple times.

The other thing to do is to run all the time on reserve, or even better? Pull your petcock, and yank out the cooper reserve tube. Then it's always on. If your racing the bike all the time, getting some foam baffles in the tank can also help keep the fuel from sloshing around and causing "issues" on long corners.
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Charles Gallant