Throttle Prop System

During deceleration (high manifold vacuum) wet fuel is drawn off the intake manifold walls and gives a rich air/fuel ratio and poor combustion. To compensate for this condition, the throttle prop system opens the throttle valve to reduce manifold vacuum and admit additional volumes of air. This provides a more correct air/fuel mixture for better combustion. System operates as follows:

1. A trigger valve is connected to the intake manifold by a pipe. Under high manifold vacuum a diaphragm in the trigger valve is pre-set to lift at 22.5-23" Hg.
2. This vacuum is relayed to a vacuum servo unit equipped with a spring push/pull link. The vacuum moves the diaphragm and causes the spring link to open the throttle prop lever.
3. The throttle prop lever holds the throttle valve open a slight amount until vacuum in the intake manifold drops to about 18" Hg. Trigger valve then closes and movement of the vacuum unit closes the throttle valve. An air bleed pipe from the air cleaner elbow to the trigger valve allows atmospheric air to replace the vacuum after the valve diaphragm closes.