<HTML>Getting a bigger cilynder and piston will really boost power, but what you should also consider is a bigger carburettor. If you have a bigbore-kit in combination with a tiny carb, you wont get much extra power out of it. Upgrading my 50cc fourstroke from a 12mm carb to a 16mm gave me 20 extra kph, that's about 12-13 Mph. Most people with the same moped as mine have a 19mm. When you're getting a bigger carb, be sure it comes with a good manifold, a manifold that's too small will render a bigger carb useless. When you get a bigger cilynder and piston, you should also get the right cilynderhead to go with that size. a 70cc with 70-head and 19 or 20 mm. carb will go almost twice as fast as a 50cc with a 10 or 12 mm. carb. (well, with my bike it does, I have a 1974 Honda SS50)
Also after installing all this, you should get a race-exhaust, because the exhaust will then be the part holding you're bike back the most.
Other things to do would be installing an advancing ignition and a race-crankshaft, and ofcourse yanking out all the restroctors.
P.S. If they ask $350 , they're really ripping you off !! $100 for the cilynder and $80 - $100 for the piston, no more.</HTML>