The Rover-Landers of BC

Carburetter throttle-prop system
Under high manifold depression, that is, on engine overrun with rapid throttle closure, wet fuel is drawn off the inlet manifold walls and gives a rich air/fuel ratio and poor combustion. To compensate for this condition a system is employed of propping open the carburetter throttle butterfly to reduce the manifold depression and admit sufficient volume of the correct air/fuel mixture to give good combustion.
1 A trigger valve is connected to the inlet manifold via a pipe.
2 Under high manifold depression a vacuum is formed in the trigger valve lifting a diaphragm from its seat which is pre-set to lift at 20.5 to 21.5 in. Hg.
3 The depression is relayed via a pipe to a vacuum servo unit.
4 Attached to the vacuum unit is an adjusting rod.
5 A spring push/pull link is attached to the vacuum diaphragm.
6 The depression moves the vacuum unit diaphragm with subsequent movement of the spring link and throttle-prop lever which opens the throttle butterfly a small amount. This position is maintained until the vacuum in the inlet manifold drops with the decrease in engine speed to approximately 19 in. Hg when the trigger valve diaphragm closes and movement of the vacuum unit closes the throttle butterfly.
7 An atmospheric bleed pipe from the air cleaner elbow to the trigger valve allows clean air at atmospheric pressure to replace the vacuum after closure of the trigger valve diaphragm.