25-30cc weedwacker engines have enough power to run a 20 inch bicycle with a fatass teenager(old me haha) at about 18-20 mph. That was prob more a limit to gearing as the engine was def redlining. Im pretty sure 25 or 30 was possible. Im going to start constructing something very soon, at first just a motor powered bike but later i will build aero bodywork
http://ecomodder.com/forum/showthrea...a-14759-3.html