i dont think its the cdi holding it back, i have my stock cdi on and just chucked a tbv2 head on and now it revs much higherMine revs fairly well, to make it rev more put a different CDI on it to increase or take away the rev limiter. Then need stronger valve springs. Stock YX springs are too soft and can valve bounce easy, not that I ever valve bounce mine.
How old are you mate? been riding long?
so the valve springs is all you would have to do imo