Anti-AFTERBURN Valve
At the beginning of a sudden deceleration, a rich air/fuel mixture is present in the intake manifold and is supplied to the cylinders. This excessively rich mixture does not completely burn in the combustion chambers and may cause an afterburn (backfire).
To prevent such partial combustion, the anti-afterburn valve supplies fresh air to the intake manifold during periods of increased manifold vacuum to reduce the overly rich mixture. The valve is sensitive only to sudden increases in intake manifold vacuum and remains open in proportion to the amount of pressure change sensed by the diaphragm of the anti-afterburn valve.
A check valve and fixed orifice are built into the diaphragm. The check valve allows air to flow only from the sensing chamber to the air chamber. If the vacuum in the sensing chamber, which is connected to the intake manifold, decreases, the check valve opens to allow air into the air chamber until the pressures in both chambers equalize. In the event of a sudden increase in manifold vacuum, the entire diaphragm unit is pulled downward. This condition lasts for a few seconds until the pressure in both chambers in equalized by air entering through the metering orifice.