take a fast clutch and i don't know how to put this in english but in holland we caal it a vario then you can tune your cilinder but the easy est way is to put in a 70cc
try using harder (tighter) clutch springs to let the engine reach higher rpms before the clutch engages, the clutch springs are the small springs that prevents the clutch from engaging
if you want a fast takeoff you'd better get a race clutch & clutch bell, Malossi offers an excellent clutch which is called Delta clutch which really works well under racing conditions.