Re: ideas for the rear wheel
i've got all sorts of ideas like that, too. i was looking into flip flop hubs and left side drives, because i wanted to make a rear freewheel on the engine side.
as far as i can figure out, you'd need a pull start because it'd freewheel when you pedal it, but it would cause a lot less wear on the gears because the engine would freewheel while coasting, so your chain wouldn't be moving all the time when you're clutching. like coasting down steep hills your chain wouldn't be going crazy.
they used to make a locking freewheel system, but from what i've read, they were prone to failure and probably wouldn't hold up to a motor.
i've also thought of threading on a sprocket to a flip flop, but an aluminum sprocket would probably rip the threads right off under power,, so you'd have to go steel, and probably make the sprocket thicker at the bottom with more threads.
i remember my old Honda CT90 had sprockets on both sides of the hub, so you could flip the wheel around. lower gear for trails and higher gear for street. haven't found one of those bikes to look at to see if it could be adaptable, i know most mopeds and trail bike hubs are a lot wider than bicycles.
i'm sure someone will come up with a system. i think the guy who made the Cylcone replica had a set up with two sprockets and it spun the threads off...