Fiero L4-151 2.5L (1985)
Vacuum Spark Delay Valve: Description and Operation
Vacuum Advance Delay
This valve controls exhaust emissions by delaying vacuum advance under some acceleration conditions. This valve is located in line between the
carburetor and distributor vacuum advance.
During light acceleration, the ported park signal to the vacuum advance diaphragm is delayed by the spark delay valve which causes the vacuum
advance to delay during acceleration. During cruising conditions with no change in vacuum, the restrictor does not affect vacuum advance. During closed
throttle and heavy acceleration conditions when the ported vacuum decreases, the pressure differential across the restrictor disc reverses and causes the
choke valve to open so that transfer of the decreasing vacuum signal is not delayed by the resistor disc.