RE: Motorized Bikes???
Seems to me like its already been done, I own an XR200 (Honda 4-stroke) dirt bike. Its quite, takes straight gas, and has the bottom end power to drag, whats the advantage of your friends "invention" over my tried and tested dirt bike???
That being said I too prefer to walk and only use the bike occasionaly when the alarm doesn't go off and I sleep in.