Vacuum Throttle Positioner: Operation

The speed switch receives an ignition pulse through the ballast resistor, which is connected to the ignition control unit. It senses when engine speed is above 2, 000 RPM, and energizes the throttle positioner. By energizing the throttle positioner. The plunger extends slightly and will hold the throttle blades open to 1750 RPM on sudden deceleration. This will prevent an overly rich mixture during deceleration.

When the speed switch senses that engine RPM has dropped below 2000 RPM, it de-energizes the positioner and throttle blades are allowed to return to normal idle position.