How do you make a 49cc pocket bike go faster?

this might help some onethis is as far as i got i put a new performance muffler on it,performance air filter on it and i took all the ex weight i,it go close to 48-51 my best bet is to put chainsaw enginie on it then you will go about 65-80 with more power cuz the mini pocket bikes don't have direct drive/ its a slow take off with a chainsaw enginie you have a burn out take off that's the best thing to do