Hi Joe,
Believe me...I have never had any desire to make one of these engine powered bikes go fast, until recently. This is based on a customer request, and he fully understands the risks of racing.
I haven't even messed around with trying to tune one of these for perfomance until now. Honestly, they are fast enough for me as they are.
This week, we hit 40 mph, (Gps), with very little modification. Very little in my book anyway. It is a 26" beach cruiser bike with a 40T rear sprocket. I'm sure the next 20mph won't be a problem. The bike still accelerates "hard", so I could just step down the rear sprocket and hit 50mph with an engine that is still soggy. We can all laugh about the Chinese 66-69cc engine...but the fact remains that this is a 66-69cc engine. I had a heavy, (compared to a bicycle), T/C 90cc Suzuki enduro when I was a kid that would go 75mph.
None of what I do to make this bike fast will be for sale to the general public. The very thought of a kid bolting a high powered engine to a $89.00 Huffy Cranbrook doesn't give me the warm fuzzies, if ya know what I mean.
The parts I offer are geared toward making the total package smoother, safer, and more rideable. My product designs will continue to be geared towards solving problems that make building and riding a Motorbike more fun. I've got a long way to go; but ultimately I will have a variety of products that will offer the builder an alternative to the kit supplied hardware. The stuff I make is not for everyone...but it is available as an alternative.
Jim