Cadillac 54-6219 1954 Shop Manual page 239

12-8
ENGINE FUEL AND EXHAUST
of the fuel in the bowls at all times. Since the same
pressure which causes air to flow into the carbure
tor also causes fuel to flow, the restriction offered
by the air cleaner does not influence the fuel air
ratio metered by the carburetor. A connecting
passage along the outside of the bowl casting tends
to equalize the vapor pressure between the two
bowls. Fig. 12-9.
The atmospheric
idle vent allows vapors to
escape from the carburetor bowls to the outside
air, under conditions of idling or stopping the en
gine when hot. Refer to Fig. 12-10.
Idle Circuits
Fuel for idle and early part throttle operation
is metered through the low speed circuits of the
primary side of the carburetor, shown in Fig.
12-10.
Discharge of fuel from the idle ports in the
throttle body continues as the primary throttle is
opened until the vacuum at the main discharge
nozzles becomes great enough to draw fuel through
the main system.
In idle and early part throttle operation, fuel
enters
the main wells from the primary bowl,
through the metering rod jets on the primary
side of the carburetor, and is drawn up through
calibrated low speed jets at the bottoms of the
idle tubes. These low speed jets measure the
amount of fuel to be used.
The fuel is then drawn up and air is bled through
the by-pass restriction. This mixture is drawn up
and through the cross-over passage in the bowl
cover. The mixture then passes through a cali
brated economizer restriction which retards the
flow to allow additional air to be mixed in at the
air bleed passage in the bowl. The rate of fuel
flow through the economizer determines the amount
of air which enters the air bleeds.
After the fuel is broken up and mixed with air
in this manner, it is conducted down through
passages in the bowl to the fixed and adjustable
idle ports in the two primary throttle bores.
The fixed idle ports
are vertical slots which
extend partly above and partly below the primary
throttle valves at normal idle and very early part
throttle conditions. The size of the idle port below
the valve which feeds the fuel mixture thus in-
SECONDAR'
SIDE
Fig. 12-9 Carter WCFB Float System
Fig. 12-10 Carter Carburetor Low Speed Circuits