Originally Posted by dabac

My cousins, who lived on a farm, had welders and discarded chainsaws and stuff laying around, tinkered with stuff like that.
Me, apart from the fun of the build, I never saw the point. Motorizing a bicycle creates a poor bicycle and an even poorer scooter/moped.
But I guess it'd make a little bit of sense if you do want a scooter, but is worried about running out of gas.
I beg to differ.. a poor bicycle, sure, because it adds 25 lbs and a ton of extra drag from the engine sprockets. but it has WAY better power to weight ratio than a scooter, meaning I would still be able to take it off road, get better mileage (approximately 300 miles/gal), and I probably don't have to worry about registration and insurance, until someone tells me otherwise.. I've seen these things in Austin, and none of them have license plates..

Keep in mind that laws generally aren't open to debate. The risk of being stopped and checked might be low, but if it happens, don't expect to get away on account of being "almost" legal.

Don't understand that bit about "sounding like a tractor". Tractors will rev a lot less than your 80 cc. Aren't these two-stroke? Do you want it louder? Quieter?
would like to have it quieter

Unless you're riding in a perfectly matched tailwind, 2-stroke is no health concern for the rider. But you will be spewing unburnt fuel all along your route.