hesitation?

Fully stock. It kinda did this before I removed the screw with the spring on it that makes it go slower. After I removed that screw it was fine. Now it seems to be doing it again. Ideas on why it won't stay steady? What can I try? Doodle bug db30 full throttle hesitation - YouTube

Hi, I have a 3HP on the Bird and a 5HP on the Clark Kart. Both of them hesitate and stumble on full throttle. What's the cause? Idle mixture is; in until it stumbles and then back a bit? Thanks, Cam