Mixture Control Solenoid
The carburettor's air / fuel ratio is controlled, via the ECM, by the mixture control solenoid.
The mixture control solenoid has an air bleed in its top and a fuel jet in its bottom. When energized, the jet is closed and the bleed is opened. When de - energized, the solenoid returns to its normal state where the jet is open and the bleed is closed.
The longer the solenoid is energized, the leaner the air / fuel mixture will be.
When the (O2) sensor sends a low voltage (0.1 V) indicating a lean mixture, the ECM de - energizes the mixture control solenoid letting it return to its normally open state. By actuating the mixture control solenoid the ECM can therefore regulate the air / fuel mixture to minimize emissions.
The carburettor is linked to the ECM by this closed loop circuit. If a failure occurs in this circuit, the primary main metering system will operate in a full rich condition until the failure is repaired.