When the throttle plate is advanced to a point just above the idle range, the volume of air passing through the carburetor creates a suction at the tip of the main discharge jet. With the float chamber vented to the air intake pressure, the greater pressure in the float chamber will cause fuel to flow from the fuel bowl through the main jet, into the metering well and dischrage jet where it is mixed with air taken in through the well vent jet at a point below the level of the fuel in the main discharge jet. This fuel-air mixture from the main discharge jet is discharged into the air stream through the secondary venturi and mixed with more air as it passes through the main venturi