The fuel flow through the metering system is controlled by the engine vacuum.At cruising speed, the fuel flows from the float chamber through the main jet, which measures or meters the fuel, into the bottom of the main well. The fuel moves up the main well and past the narrow air bleed holes in the side of the main well tube. Air, which enters the main well tube from the main well air bleed, is added to the fuel by these air bleed holes. This mixture of fuel and air, being lighter than raw fuel, responds faster to any change in venturi pressure differential. It also vaporizes more readily than raw fuel when discharged in the air stream in the venturi. Additional air from aspirating nozzle enters the fuel as it passes from the top of the main well to the vertical passage leading to the nozzle tube. This mixture of fuel and air is then discharged into the air stream in the booster venturi. The throttle plate controls the amount of fuel air mixture admitted to the intake manifold, regulating the speed and power our put of the engine in accordance with accelerator pedal movement. The main metering system passages for both primary barrels of this carburetor are identical and they function simultaneously as described.
