Mixture Control Valve--Non Calif.

Fig. 18 Mixture control valve.:

The purpose of the mixture control valve, Fig. 18 is to prevent backfiring in the exhaust system during deceleration. The mixture control valve is designed to supply air into the intake manifold to prevent over enriching of air-fuel mixture, when the throttle valve in the carburetor is suddenly closed.
The mixture control valve is held closed under normal operating conditions. When the vacuum in the intake manifold increases rapidly, the valve opens, allowing the air from the air pump into the intake manifold.