The intermediate speed and high speed circuit consists of the Metering Rod (M), Metering Jet (N), Nozzle (0), and gasket, Throttle Valve (J), and Metering Rod Spring and Disc.
As the throttle is opened wide enough for a speed of a little more than 20 m.p.h., the velocity of the air flowing down through the carburetor throat creates a pressure slightly less than atmospheric at the tip of the main nozzle.
Since the gasoline in the float bowl is acted upon by atmospheric pressure, the difference in pressure between the two points causes gasoline to flow from the bowl, through the metering jet, and out the main nozzle into the throat of the carburetor.
As the speed increases from 20 m.p.h., the high speed system continues to cut in more and more and the Idle or Low Speed System to cut out until the High Speed System is carrying the entire load and the Idle System is doing nothing.
At higher speeds, the area of the opening between the jet (N) and the Metering Rod (M) governs the amount of gasoline going into the engine. At top speed, the smallest section of the rod is in the jet.
