[robbiescd]

Check the vent on the carb. It's next to the adjustment screw....a little silver nipple. It normally has a plastic tube going from from to the it. I had a cart doing something similar and when I pulled the tube off, it ran great. Plug it up, it ran bad. Took my air hose and blew out the plastic line. Something came out! Plugged back up and ran fine.

Had the same issue with another cart, but it had no tube connected. Took some carb cleaner with the straw on it and stuck it in the little hole. Blew it out and runs fine now.

If neither of those are the issue, I agree with previous post.....rev limiter.