This is the Microbike... I built this back in 2004-2005. This was just before I met Ash. I had a lot of time on my hands.
It originally was a Runt bike, which I strapped an engine to the back with friction drive... it was fun, but I wanted to go smaller. I hacked the frame in half, got rid of the rear suspension and bolted the swing arm on solid. Welded a seat mount to the remainder of the frame. Wheels are goped wheels, which fit well with spacers. Rear wheel is specifically from the Goped GSR (Chain drive model), as you can bolt a sprocket to it. Engine mount was fabricated from weldable steel from Lowes. Engine is a 31cc ryobi weedeater engine, with the covers removed. Flywheel fins were ground down to make the flywheel thin enough to fit in the mount. Front sprocket is the smallest pocket bike sprocket I could find...6 tooth. They come ready to thread onto the clutch they normally mount to on a pocket bike. The ryobi did not have these female threads to accept the sprocket, but does have a long extension off the crank. I cut male threads into the crank. I then found 2 nuts that each thread onto the crank, and the sprocket. I welded these together as straight as I could. It took a couple of attempts, but eventually ended up with a perfect adapter. Adapter screws onto crank, and sprocket screws onto the adapter. I added axle pegs to not only put your feet on, but to also protect the bike from falls. Fuel tank is off some weedeater, I don't remember... added a twist throttle, and modded the exhaust so it didn't shoot into your leg. The seat is a Harley backrest
That's about it! No brakes. No kill switch. No clutch. Direct drive... You push start it, then jump on while its moving. I takes quite a bit of practice to get it right. It is also rear heavy, and likes to wheelie over if you aren't leaning forward. It does about 20mph, which is PLENTY fast for its size. It always seems to gather a crowd when I ride it in public areas. Its also been a tough little bugger... Been wrecked MANY times by different people, and can always be picked back up and ridden again.