twisting

I'm finishing up my mini bike project, and I have the throttle not retracting smoothly. As in after twisting the throttle open, it doesn't want go back closed on it's own. Any suggestions?

My coleman ct200u is making a grinding noise and is pulling like im twisting the throttle.

I bought a used Baja Doodle Bug DB30 yesterday. The pull starter is missing, but I am able to get it to start using just the rope. Anyway this is the first mini bike I've ever own. I have a quick question, is the mini bike supposed to pull without the twisting throttle because mines does...