As the throttle is advanced to approximately one-quarter opening, the amount of air passing through the venturi creates a suction on the tip of the main discharge jet. This suction causes the fuel to flow from the fuel chamber through the main jet and into the main discharge jet where it is mixed with air admitted by the well vent jet. This mixture is then discharged into the air stream through the discharge jet. The main jet controls the fuel delivery from about one-quarter to full throttle opening. To maintain a proper mixture ratio a small amount of air is admitted through the well vent into the discharge jet through air bleed holes located in the discharge jet at a point below the level of fuel in the metering well.