Abstract: A motorized bicycle, uses a bicycle-type frame, having a front wheel and rear wheel rotatably attached thereto. A horizontal shaft internal combustion engine is supported in the frame and linked to a drive train with a pedal actuated or automatic clutch, for selectively allowing the engine to be engaged to drive the rear wheel. The drive train may include a number of pulleys and belts or sprockets and chains. A throttle is provided for controlling the engine, and brakes are provided for slowing the wheels of the bicycle.