Not to mention the weight and heft a 4 stroke would bring. Sure, low end torque but no RPMs so the gearing would be very limited. You would probably need to design your own gears, maybe make some spurs into poinions. If I were to build something with a 4 stroke, it would be one of these motors.
http://www.youtube.com/watch?v=J3y8C...eature=related