Throttle

The throttle controls the air flow into the engine. In the photograph it is shown in the full open position. In this position there is no throttle obstruction to air passage through the inlet manifold. As the throttle is closed down (Rotate the knob shown) it starts to obstruct air entry to the inlet manifold and causes a pressure drop in the inlet manifold. This reduces the total oxidizer supply brought into the engine during the intake stroke.

Because this engine has mechanical fuel injection, the fuel supply is independent of the air flow. Closing the throttle also alters the Air-fuel ratio.