Vacuum Spark Control Delay Valve

This valve is used on 4 cylinder engines to improve driveability when the engine is cold. It is located in the vacuum advance circuit. When vacuum is greater at port "4" than at port "1", air must flow through the orifice to equalize the pressure. This creates a momentary delay that prevents a sudden decrease in spark advance. When vacuum is greater at port "1" than at port "4", air flows freely through the check valve and pressure is instantly equalized.