Dual Diaphragm Distributor: Operation

The outer diaphragm is coupled to the movable breaker plate. An increase in vacuum pressure moves the diaphragm against advance diaphragm spring tension, causing the movable breaker plate to pivot opposite to distributor rotation. Thus ignition timing is advanced, and this is to occur during normal road-load operation, but not during deceleration or idle. When intake manifold vacuum is applied to inner diaphragm (retard) it moves inward toward the distributor. This allows the advance diaphragm to move, causing the movable breaker plate to pivot in the same direction as distributor rotation. This retard of ignition timing automatically occurs during engine idle or deceleration.