Idle System

When throttle valves are closed, vacuum from engine draws fuel from emulsion tube and the fuel mixes with air from the metering jet. The mixture flows into the carburetor barrel downstream of the throttle valves by way of an opening between the orifice and tapered end of mixture screw. Upstream of the throttle valves, two orifices called "Progression Holes", supply fuel to provide mixture when throttle valve is opened. When throttle valve opens, vacuum by the idle port decreases and is insufficient to draw enough mixture for proper operation. The "Progression Holes" supply this mixture before the main jet system comes into operation.