If you're not planning on doing much to it then a Toomey B1 would probably be pretty good. If you have big plans then Get a Factory7 (or any of the other pipes made by power pros) or a dyno port
well its my couzins blasty i just have a hollowed out stoke which is incredible
and a can off a 89 kx 125 that i shortend up 4.25 inches ans made a sick stinger and it pulls hard like the cpi