The main metering system controls the flow of fuel during the immediate or part throttle range of operation. With the throttle valves in a partially open position, fuel flows from the float chamber through the main metering jets and into the main discharge jets where it is mixed with air taken in through the high speed air bleeders. This mixture of air and fuel is then discharged into the air stream through the auxiliary venturi tubes. The main body and main discharge jets are so designed that should vapor bubbles form in the fuel in the main discharge system, due to high temperatures, the vapor bubbles will collect in the outside channel surrounding the main discharge jets, rise, and vaporize in the domes of the high speed bleeders thus preventing percolation.