you mean top end speed ????
try a bigger 14 tooth front sprocket, but in that case your existing chain will be about 2 full links too short, thay have chain and sprocket kits on ebay for around $60 that include a new chain, 14t front sprocket and smaller rear sprocket, the ad will say "more speed"
if your talkin quickness/more power on the trails, an aftermarket pipe/silencer, uni or k&n filter, and rejet the carb will be your cheapest route, but still $2-300 with a used pipe