1975-76 Automatic Transmission Equipped Models

At temperatures above 149°F (65°C), thermo sensor is open and solenoid is de-energized. This allows manifold vacuum to enter retard side of distributor vacuum diaphragm. This is not continuous, as vacuum bleeds through delay valve. Eventually, valve is tripped and retard vacuum is dumped. At temperatures below 149°F (65°C), no ignition timing retard takes place. Ignition timing is advanced or retarded depending upon vacuum at carburetor ports and delay valve, regardless of engine temperature.