I got a totaled scooter free and put the engine on the back of my mountain bike with a small aluminum frame that i built with only a hack saw and a hand drill in my living room. There was no welding or anything, everything is drilled and bolted. It can do 50mph on flat ground but is smooth with no vibration about 35. it uses the scooter drum brake for the rear and bike v brake front. i left the e start intact so i dont have to kick it.
The gas tank is a normal bicycle tank mounted inside the bag on the seat post. The intake had to be modified to be the right angle. I cut the battery box out of the scooter and mounted it close to the tire. The only bad part is it like to pick up the front tire because all the weight is in the back. On the other hand most of the engines weight is not on the bicycle frame, the engine basicly supports itself. the engine is a clone of the zuma. The frame is held to the bike with clamps i made that dont affect the frame so I can put the bicycle back to normal if I want to. The best part is I only spent $80 on the entire project, I had to buy the alumium, gas tank, threaded rod +nuts and bicycle lights
