I just signed up here to learn more about these engine powered bicycles. I have been riding bicycles on and off since 1954. I always love anything on 2 wheels, which includes motorcycles too. When my oldest son was about 5 years old, I modified (lowered) an old Junker 20 inch Schwinn, Stingray bike so he could ride it. I made it look like an old board tracker. In the 70s I worked as an R&D tech. for "Triple A Motorcycle Accessories" in Gardena, CA. We did all the prototype work for Kawasaki's All aluminum frame 20" racer motocross bicycles and eventually manufactured them too. I also have ridden motorcycles since 1963. I still ride motorcycles. I have been interested in these motorized bicycles for about 20 years, now that I am retired (Worked as a Tool & Die Maker) I want to build a 4 stroke engine powered bicycle. Probably use it to make trips back and forth to the liquor store, Dang, I just remembered there are no liquor stores here in Utah. At least not like the ones in California. I want to make my motorized bike look retro styled, like the old timer early engine powered bicycles from the 1900s. Anyway I am looking forward to learning a lot from all you experts out there.