The idle system delivers 100% of the idle fuel. It also meters fuel at off-idle throttle positions; a large percentage at just off of idle decreasing to a minor influence as the throttle is opened wider. The idle setting is critical both to a smooth idle at proper rpm and to a smooth transition to part-throttle operation.

Fuel is drawn through the idle system by the intake manifold vacuum tat is communicated at the idle screw port and transfer slot. Fuel in the bowl passes through the primary main jet and metering rod restriction and into the primary well. The fuel for the idle system is drawn through the restriction at the end of the idle jet - a brass tube - and flows up the tube to the location of the first idle air bleed - a brass restrictor - where air is mixed with the liquid fuel.

The emulsified air and fuel is then drawn through the idle channel restrictor - a drilled passage that serves to increase the velocity of the air and fuel to promote better mixing. As the emulsified fuel is discharged from the idle channel restrictor, additional air is added at the second idle air bleed - a drilled hole - and the highly aerated mixture then moves through the passages in the main body to the location of the transfer slot and idle screw port. The transfer slot is a large air bleed when the throttle is closed, but as the throttle is opened the slot is exposed to manifold vacuum and becomes a discharge port for idle system fuel. The idle screw port is a variable discharge restriction that is adjusted by the engine tuner to achieve the desired air fuel ratio at engine idle.