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The secondary air valve in a Quadrajet allows it to function like a variable venturi carburetor. It adapts the airflow and fuel delivery characteristics of the carburetor to the air load demand of the engine differently than conventional designs. Effectively, the greater the demand the larger the carburetor to the limit of 800 CFM. The load controlled air valve was the game changer for the QJ, making it very adaptable and broadly applicable to the entire GM line.