Affordable Go Karts - Home page - AGK - http://www.affordablegokarts.com
is another place to get loads of High Po parts and mod instructions for these engines,
I built one of these 6.5 HP GX200 clones winter before last, installed custom billet Con Rod, flat top piston, 14cc combustion chamber GX160 Head, 1.2 Ratio Yahaha Rocker arms, Advanced the ignition timing 6 degrees and built a custom exhaust pipe for it, and of coarse had to rejet the stock carb.
I had it on a home built Go Kart and with a 15T noram racing clutch driving a 60T sprocket on 13.5" rear tires it would hit 50+MPH, I have since taken the engine and put it in the shop until I can get a billet flywheel on it and a custom intake with a tilitson carb.
These are very powerful engines but at high RPM's they vibrate real bad, personally if I could not get it balanced to be smooth at the higher RPM's I would not remove the govenor from these engines and just let them top out at around the 3600 - 4000 RPM mark, My engine in it's current state would trash a bike frame from the intense vibrations IMO, the custom Billet flywheel might be a cure but cant say for sure, also the torque these engines produce will likely be a destructive strain on a standard rear wheel axle, I could be wrong on this but these put out a lot of power when even slight mods are done to them and they're tuned right. build that frame up with some bracing in the key areas and be very careful with this engine on a bike, it could be a death trap or a super awesome ride, just depends on how it is all put together, dont build the engine for the bike on this one........build the bike for that engine......! Good luck!
Do it right and you'll have a heck of a ride, I have been thinking of doing this very same thing with a stock 6.5 Clone, I have a couple old Comet Torq-a Verter set ups and with this engine just stock, it would make one heck of a Motorized Bike IMO.
Just my $.02 nothing more, nothing less!