Vacuum Advance Spark Control

Used on all carburetor models, this system provides increased spark advance during cold engine operation. When engine coolant temperature is below 100°F (38°C), thermal vacuum switch (TVS) closes. Manifold vacuum is supplied to distributor through delay valve, which holds vacuum at high levels during acceleration. Above 100°F (38°C), TVS opens, causing manifold vacuum to by-pass delay valve.