I had a similar problem on mine. Turns out my motor mounts were loose, and the increased vibration shook up the carb so much that the carb bowl wasn't filling with enough fuel. Took me couple weeks to figure that one out.

Try tightening your mounts, and if that doesn't fix it, check that your carb is filling properly.

__________________
-Herman

"Do not take life too seriously. You will never get out of it alive." -Elbert Hubbard