1600 Models & 1800 Hardtop, Hatchback & Sedan Models With 5-Speed Man. Trans.
When intake manifold temperature is between 59-95°F (15-35°C), thermal vacuum valve opens distributor lines to atmosphere. No advance is applied. When engine is operating above or below these temperatures, vacuum is applied through check valve and obtained at a below-throttle vacuum port (with engine idling) or applied through orifice and obtained at an above-throttle vacuum port (engine above idle).