i have this problem but its at realy low revs its when i pull off on bitting point it vibrates the soon as i twist back its fine it hassent affacted the bikes mid and high revs as i twist it goes a hang on for dear life lol, im thinking it could be either fuel tap as if i turn it to full tank it cuts the fuel, so i have to ride in reserve ive just put redex in the tank so ill see if that works im goin to change plugs, im gonna try simple things untill it will require proper tools and proper mechanic but bike r pretty simple neway