I picked up a PK80 from Zoombicycles last winter as something to fool around with and keep me busy during the winter months. Of course I found this (my favourite) and other forums on motorized bicycles and my interests perked. The quality of the kit at first looked bad, due to the rough castings, but after tearing the engine apart I was impressed. For $120 shipped (smoking deal at the time) this thing seemed put together all right. I went ahead and put locktite on all the bolts, and upgraded ones I felt might need it. I bought a brand new decent quality wheel from a bike shop, then I trued the wheel and tensioned their spokes, mounted the sprocket and rag joint, then trued and tensioned again. The sprocket and rim still run dead true today. I rigged the clutch to the left grip shamano trigger shifter because I didn’t want to mess with two leavers. I setup the bike as a single speed, and kept the detailer just to tension the pedal chain. Since the frame I used had horizontal dropouts, I didn't use a chain tensioner for the engine drive chain.
When I first got it running I was unimpressed. It was very difficult to start, vibrated badly, fouled plugs, and used up a lot of fuel for such a small engine. The project sat at the corner of the garage for a wile.
Then I began to tinker with it a little, and once it loosened up a bit, and I got the mixture so the plug was just right I started riding it. I put a cardboard cut-out behind the clutch cover and that quieted it down a bit. Then the more I rode the bike, the better it ran. I've got about a gallon and a half of gas though it (24:1 from day one) and its starting to run like a top. It has smoothened out substantially, and it starts up right away. It has the power to pull my 260lbs up the steepest hills around here without even trying.
Non-electric motorized bicycles are very much illegal around here so I've been a little worried to ride it around, but so far so good. I guess a middle aged man putting along at bicycle speeds or slightly faster (15-30km/h) doesn’t look menacing enough. I passed a police officer sitting in his cruiser in a school parking lot. My heart raced as I putted passed him at maybe 25km/h but he didn’t flinch. Lets hope the attitude doesn't change.
All I can say for now is so far so good!