The idle system as shown in Figure B, consists of two idle discharge holes, idle air passage, idle adjusting
needle, idle jet, and fuel pick-up passage.
The fuel for idle is supplied through the main jet to a well directly below the main discharge jet. The pick-up
passage is connected to this well by a restricted drilling at the bottom of this passage. The fuel travels
through this channel to the idle jet calibration. The air for the idle mixture originates back of (or from
behind) the main venturi. The position of the idle adjusting needle in this passage controls the suction on the
idle jet and thereby the idle mixture. Turning the needle in closer to its seat results in a greater suction with
a smaller amount of air and therefore a richer mixture. Turning the needle out away from its seat increases
the amount of air and reduces the suction, and a leaner mixture is delivered. The fuel is atomized and mixed
with the air in the passage leading to the discharge holes and enters the air stream at this point.
HIGH SPEED SYSTEM
The high speed system, Figure C., controls the fuel mixture at part throttle speeds and at wide open throttle.
This system consists of a venturi, controlling the maximum volume of air admitted into the engine; the main
jet, which regulates the flow of fuel from the float chamber to the main discharge jet; the well vent, which
maintains uniform mixture ratio under changing suction and engine speeds; and a main discharge jet, which
delivers the fuel into the air stream.
The main jet controls the fuel delivery during the part throttle range from one-quarter to full throttle
opening. To maintain a proper mixture ration a small amount of air is admitted through the well vent into the
discharge jet through the air bleed holes in the discharge jet at a point
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