A gear box power control system is disclosed to be consisting of a centrifugal clutch with integral bell housing drive, a gear train for speed reduction and torque enhancement, an output jackshaft with an engaging system to disengage and engage engine power to a primary drive sprocket for chain operation. The engagement and disengagement of engine power is done by an integral engager remotely controlled by steel cable and hand lever. A motorized vehicle is disclosed as consisting of a standard bicycle frame or modified bicycle frame, a tricycle frame, a go-cart frame, and a paddle wheel boat frame all with the gear box power control system of present invention installed on a gasoline four cycle engine.