Spark Delay System

When engine coolant temperature is below 95°F (35°C), the Thermostatic Vacuum Transmitting Valve (TVTV) is open and normal vacuum advance is allowed. When coolant temperature rises to 140°F (60°C), the TVTV closes, forcing vacuum to flow through spark delay valve. Vacuum must flow through a small orifice in valve, delaying time when full vacuum advance will occur. When intake manifold vacuum drops, check valve opens, allowing vacuum advance to release immediately.