An engineís ignition system controls the spark that ignites the fuel in a cylinder. Smaller displacement engines for off-road use typically have a kick-starter, a starter crank activated with the riderís foot. Larger displacement engines and those designed for street use have an electric starter activated by turning a key in the ignition and pressing a starter switch.
Riders regulate motorcycle speed with a twist-grip on the right handlebar called the throttle. Twisting the grip backwards opens a throttle valve in the engine, increasing the amount of air and fuel that enters the cylinders. In older motorcycle engines, twisting the throttle increases the amount of fuel and air pulled into the carburetor, a device that mixes the fuel and air before it is delivered to the cylinders for combustion. Many motorcycles built after 1990 have fuel injection systems instead of carburetors. A fuel injection system uses computer-controlled fuel injectors to spray measured amounts of fuel into each of the engineís cylinders.