Ignition System: Description and Operation
Fig. 41 Ignition timing control system. Prelude w/carbureted engine:
This system, Fig. 41, is designed to improve driveability at cold engine temperature by advancing ignition timing. The vacuum control solenoid valve is operated by the control unit which receives signals from the intake air temperature sensor and thermosensor. When vacuum control solenoid valve opens to introduce manifold vacuum to the vacuum advance unit, the distributor breaker plate is turned and ignition timing advanced.