Vacuum Advance Delay

PURPOSE
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.

OPERATION
During light acceleration, the ported spark Signal to the vacuum advance diaphragm is delayed by the spark delay valve which causes the vacuum advance to delay during acceleration.

During cruise conditions with no change in vacuum, the restrictor does not affect vacuum advance.

During closed throttle and heavy acceleration conditions--when 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.