Re: Hi! New member from northeast Indiana ..
I'd put a gas engine on a slightly heavy bicycle such as a Mountain bike or a beach crusier. Road bikes are made for the maximum bicycling experience and as such are not suitable for engine mounting. Pot holes, gravel, bumps in the road or sudden turns are annoying when you're on a regular bicycle- now think about that when you're going 30+ miles per hour!
Be careful, MB's are fun but they're also very dangerous- very dangerous. They're "kits" and they don't teach a driving course at Sears, they can be unfamiliar even to experienced cyclist (at first).
Start with a good bike that you can control with some weight and girth.