Carburetor: Description and Operation

Fig. 1 Exploded view of 1984 Holley model 4180-C carburetor. Other 1983-84 models similar.:

Fig. 2 Exploded view of 1985 - 86 Holley model 4180-C carburetor:

The Holley Model 4180-C, Figs. 1 through 4, is a four barrel, downdraft, two-stage carburetor. This unit can be considered as two dual carburetors, one which supplies an air/fuel mixture throughout the entire engine operating range (primary stage), and the other which functions only when a greater quantity of air/fuel mixture is needed (secondary stage).
The primary stage contains a fuel bowl, metering block and accelerating pump assembly. Each primary barrel contains a primary and booster venturi, throttle plate, main fuel discharge nozzle and idle fuel passage.

Fig. 3 Right side view of Holley model 4180-C carburetor (typical):

Fig. 4 Left side view of Holley model 4180-C carburetor (typical):

The secondary stage contains a fuel bowl, metering body and secondary throttle operating diaphragm assembly. The secondary barrels each contain a primary and booster venturi, throttle plate, idle fuel passages, main secondary fuel discharge nozzle and a transfer system fuel passage from the primary fuel bowl.
A constant fuel supply is provided to fuel metering systems by a fuel inlet system for both primary and secondary stages. A fuel balance tube is not used.