Ignition System: Description and Operation

DESCRIPTION
Ignition timing control, combined with the internal distributor control (centrifugal advance), affects the time at which each spark plug ignites the air-fuel mixture, in accordance with engine speed, load and coolant temperature. This control system gives vacuum advance in response to the manifold vacuum and coolant temperature. This optimizes ignition timing during and after engine warm-up to maximize fuel economy and engine performance.

OPERATION
This distributor has two separate vacuum advance diaphragms which operate on manifold vacuum. Diaphragm B also has a thermovalve in the line.
This system is provided to improve driveability at cold engine temperature by advancing the ignition timing. When the engine coolant temperature is below the set temperature of the thermovalve, manifold vacuum is applied through the check valve to the diaphragm of the vacuum advance unit. The thermovalve blocks the air entering the vacuum line and the diaphragms retract to turn the breaker plate of the distributor to advance the timing. When the coolant temperature is above the set value, vacuum in the thermovalve is released.