About the Engine
Old Honda made GY6.
The engine design is a single-cylinder, four-stroke engine, in a horizontal orientation. It is by fan air cooled, anf has a chain-driven overhead camshaft with a crossflow hemi head. Fuel is delivered by a constant-velocity style sidedraft carburetor,normaly a Keihin CVK clone or similar.
The ignition system is by CDI (capasitor discharge ignition), with a magnetic trigger on the flywheel. Because the trigger is on the flywheel instead of the cam, the ignition will fire on both the compression and exhaust strokes. An integrated magneto provides 12 v power for the CDI system, chassis accessories (such as lighting), and to charge a battery.
The package includes an integrated swingarm, which houses a centrifugally controlled Continuously variable transmission (CVT) using a rubber belt sometimes called a VDP. At the rear of the swingarm, a centrifugal clutch connects the transmission to a simple integral gear-reduction unit. There is no clutch of any kind between the CVT and the crankshaft; it is permanently engaged. An electric starter, backup kick-starter, and rear brake hardware is also housed in the swingarm.
The engine is now widely used in Far East scooters and ATV's