As the engine approaches cruising speed, the increased air flow through the venturi creates vacuum (low pressure area) in the venturi of the carburetor. The near-atmospheric pressure present in the bowl in the area above the fuel, causes the fuel to flow to the lower pressure area created by the venturi and magnified by the dual booster venturi.

Fuel flows through the main jet into the main well. Air enters through the main well air bleed into the. main well through holes in the main well tube. The mixture of air and fuel, being lighter than raw fuel, responds faster to changes in venturi vacuum and is also more readily vaporized when discharged into the venturi. THe main discharge nozzle passage is part of the dual booster venturi which is an integral part of the main body casting.

Distribution tabs in the main venturi provide further vaporization of the air and fuel mixture. The main metering system is calibrated to deliver a lean mixture for the best overall economy. When additional power is required, a vacuum-operated power system enriches the air-fuel mixture.