Idle Speed Control

Fig. 8 Variable Speed Governer:

With the engine running and the accelerator pedal released, the engine speed control lever is in its idle position, resting against its stop, the idle speed adjusting screw. Idle speed is chosen so that the unloaded engine runs reliably.
Control is by the idle spring on the retaining pin, which counteracts the force from the centrifugal weights. This balance of forces determines the sliding sleeve's position with reference to the plunger cutoff bore, and therefore the length of the delivery stroke. At engine speeds above idle, the spring is collapsed by the amount c, Fig. 8, and therefore no longer effective.