I'd be interested to hear more about the mods on your motors. I've calculated that this motor is good for 8000 rpm reliably, and you could squeak it to 10,000 rpm periodically. What have you found as far as safe rpm? The key issue with this motor is air flow(as with any 2-stroke). From the factory, it is unbelievably restricted and the porting leaves nothing to be desired. I've done some minor work to the head, intake, transfer ports and port matched the exhaust, with remarkable improvements over stock. Running a B-type 34mm mikuni carb(for experimenting), and still playing with the jetting. It is working very well right now, but still looking for more power. I don't have access to a dyno, but would venture to say that the power has more than doubled. I suspected that these motors could produce at least 20hp, and I hope to see your test results soon. Keep us informed.
As far as the weaknesses on the G1, be careful with the motor mounts if you're going with that much power. I am going to install a limiter strap on my motor. Also, take a look at the starter/generator if you plan on increasing the motor rpm.
COTM SEPT '06 -- 1981 G1, 4" Homemade lift, 22x11x8 tires, Custom Front Cowl. Digital speedometer. 100w AM/FM/CD. 32+mph. Looking for more power. SOLD
1989 EZGO Marathon -- 4" Homemade lift, Camo paint, 23x7x10 front, 22x11x10 rear