Ford COUGAR 1968 Shop Manual page 524

10-64 GROUP 10
-
Fuel System
the fuel-air mixture when the air flow
past the carburetor venturi is insuf-
ficient to operate the main metering
system. Air bleeds, restrictors and
adjustments are provided to control
and meter the idle fuel-air mixture.
At curb idle speeds, the throttle
plates are partially open and with
manifold vacuum below the plates,
enough difference in pressure is
created between the fuel bowl and the
idle discharge ports to operate the
idle fuel system.
Fuel is forced from the fuel bowl
through the main metering jets into
the main well. The fuel then flows up
through a calibrated restriction in the
idle tube. Filtered air enters an idle
air bleed restriction and mixes with
the fuel flowing up the idle tube. The
idle air bleed also serves as an anti-
DISTRIBUTOR VAC~JUM PICK-UPTUBE 8 2 9 8 5 - 8
FIG.
2-Autolite Model 4 3 0 0 4-V Carburetor-Left Front 3/4 View
F U E L I N L E T \
DAMPENER LEVER
CHOKE C L E A N AIR
PICK-UP
TUBE
8 3 1 6 1 - A
FIG.
3-Autolite Model 4 3 0 0 4-V Carburetor-Top View
main calibrating adjustments: float IDLE FUEL SYSTEM
level, auxiliary fuel inlet and the
external vent valve. The dual pon- The primary idle fuel system (Fig.
toons must be parallel for proper
5 )
functions when the engine is oper-
operation. ating at lo* engine rpm. It supplies
syphoning vent at high engine speeds
or when the engine is shut down. The
fuel-air mixture passes down the idle
channel into an idle cavity in the
throttle body. The idle cavity has an
upper and lower discharge port. At
curb idle (throttle plate closed), the
idle fuel-air mixture flows past an
idle fuel adjusting screw and is dis-
charged below the throttle plate from
the lower discharge port and from a
small portion of the upper discharge
port.
The upper discharge port is a ver-
tical slot-type port and extends slight-
ly below the closed throttle plate.
When opening the throttle plate. a
greater portion of the upper dis-
charge port is exposed to manifold
vacuum and a larger amount of idle
fuel-air mixture will discharge from
the upper port. Further opening of
the throttle plate results in a de-
crease in manifold vacuum and a de-
crease in the quantity of idle fuel-air
mixture that is discharged. As the
idle system tapers off, the main fuel
metering system begins to discharge
fuel.
The idle speed (engine rpm) is ad-
justed by turning the idle speed ad-
justing screw the specified turns to
partially open the primary throttle
plates.
MAIN METERING
SYSTEM
The main fuel metering system
(Fig. 6) is calibrated to supply a
leaner fuel-air mixture than other
fuel metering systems. This is be-
cause the main fuel metering system
operates during a cruise or part
throttle condition and under low en-
gine power load requirements.
Main system calibration is con-