Take a look at this homemade bike from Youtube. It's a very cool, smart setup, different than all the others. It appears that he's using a standard gokart/mini bike clutch and chain and somehow attached a kart/minibike sprocket to the crank. And I'm assuming he still has use of the bike's gears! And it's very fast, too. He's using a Honda clone engine and the only thing I'd change is to use a Robin Subaru engine instead, that is if I didn't already have a Briggs or some other engine already. Not the tiny Robin Subarus, but the larger ones that look much like the engine he's using. Anyone have any good ideas on how to attach and center the sprocket to the crank? I'd suggest doing this before making the motor mounts so the engine can be properly lined up with the sprocket. I've sent this guy a message, but most don't answer, so I'm throwing it out there.