Deceleration Valve: Description and Operation

Mixture Control Valve System:

The mixture control valve supplies air from the air cleaner to the intake manifold during deceleration to prevent excess air/fuel mixture enrichment and after burning in the exhaust manifold. The valve has a diaphragm and two chambers ("A" and "B") joined by a small orifice. The valve is controlled by manifold vacuum. When the throttle is suddenly closed, manifold vacuum increases rapidly in chamber "B" and the diaphragm opens the valve to allow air into the manifold. After a few seconds the pressure in both chambers is equalized through the orifice and a spring in the valve closes the passage to the intake manifold.