The carburetor has a diaphragm type of accelerating pump that is positive displacement in action, so that immediate pump delivery is guaranteed by the slightest movement of the accelerator pedal. The pump housing, diaphragm, jets, actuating lever and spring are attached to the bottom side of the float bowl. The pump diaphragm actuating lever is connected by a yoke within the carburetor housing to a pump lever and rod outside of the housing. This pump rod is in direct linkage to the throttle lever.

The source of fuel for the pump system originates in the float bowl. To exclude dirt the fuel must first pass through a finely meshed screen “A” in the float bowl. The fuel then travels up through the bowl passage past the intake ball check valve “B” and into the cavity in the back of the float bowl, created by the attaching of the pump diaphragm “C”. Upon acceleration, the pump actuating spring moves the diaphragm against the cavity by means of a simple rack and pinion, thereby displacing fuel. This fuel passes vertically up the passage “D” in the float bowl, past the outlet pump needle “E” and down the passageway to the pump jets “F” which spray the fuel onto the opposite edge of the main venturi to be mixed with air prior to entering the manifold.

NOTE: In the 1950 Model AA carburetor, the pump fuel is sprayed against the pump splashers, which are cast onto the inside of the secondary venturi.