Spark Retard Delay Valve (SRDV)

This valve is used to maintain vacuum advance during quick throttle openings when engine coolant temperature is below the calibration point. Above the calibration point, full manifold vacuum is used for distributor spark on vehicles without A/C or ported spark on vehicles with A/C.
When manifold vacuum suddenly decreases, the orifice within the valve delays dropping vacuum to the distributor vacuum advance. This delay is caused when lower vacuum is sensed by the valve. The length of delay is dependent on the difference between the high and low values. The greater the difference, the longer the delay.