Trapped Vacuum Spark Advance (Tvsa)

This system improves engine warm-up during heavy acceleration. A vacuum delay unit is located in the vacuum advance line and connected to the distributor Thermal Vacuum Switch (TVS). When engine coolant temperature is below the switching point, full vacuum signal is supplied through a delay valve to the distributor when manifold vacuum is increasing. A small orifice is provided in the delay valve to allow for leakdown when manifold vacuum is decreasing. When engine coolant temperature is above the switching point, the TVS opens ports 1 and 2 and full vacuum bypasses the delay valve through the TVS to the distributor.