That's kinda what I was thinking, although the dirt bike / quad engine route presents a couple issues:
1. Need to find one with an electric start, or easy to convert to electric start. Given the rear swingarm frame design, I'm not sure there is clearance for a kickstart lever to make it's full rotation unless you offset the engine all the way to the right side, which I don't want to do. I'm partial to 2-stroke motocross bikes (having ridden them in my college years) and think a 250cc bike would be an excellent donor and pretty easy to find, but I'm not sure how to address the starter issue.
2. Since the engine would be on the rear swingarm, I would need to think of a way to run the shift linkage from the engine to the main frame, keeping in mind that there is a pivot point between them.
3. Hand lever clutch on shifter linkage vs. foot clutch? I can see pros and cons for either setup.
The Tecumseh / TC route looks like a more straightforward way to go, but I don't suppose I took on this project because I wanted to build something simple!
