Fuel Supply System Operation; Idle System Operation; High Speed (Main Metering) System Operation - Ford VSG-411 Service Manual

. 3-06
Fuel System
3-06
FIG. 4b External View Manual Choke
OPERATION
Fuel Supply System
Fuel under pressure is supplied through the fuel inlet fitting,
fuel valve (needle and seat) to the float chamber. The floats in the
float chamber automatically regulate the opening through the fuel
valve (needle and seat) to maintain the proper level of fuel in the
fuel bowl and meet the demands of the engine according to speed
and load.
BOWL VENT.
PASSAGE
FUEL
INLET
w I-' "
FIG. 4c Fuel Supply System
Idle System
At idle speed the throttle plate is advanced slightly from the
fully closed position to expose the upper idle discharge holes to
engine manifold vacuum (suction), see Figure 41. This suction is
transmitted to the idle jet through a passage connecting the idle
discharge holes with the idle jet. Fuel for idle is supplied through
the main jet to a well at the base of the discharge jet. Fuel for idle is
drawn from this well through the idle fuel pick-up passage and is
metered through the idle jet calibration before entering the idle air
passage. As the fuel leaves the idle jet, it is mixed with air admitted
through the idle air bleed calibration. This fuel-air mixture in the
idle passage is discharged into the air stream through the upper two
idle discharge holes, one of which is controlled by the idle adjust-
ing needle. Turning the idle adjusting needle IN (clockwise)
reduces the amount of fuel-air that reaches the air stream to
provide a lean mixture. Turning the idle adjusting needle OUT
(counterclockwise) permits more of the fuel-air mixture to reach
the air stream to provide a richer mixture.
IDLE AIR BLEED
CALIBRATION
IDLE AIR
PASSAGE
I
IDLE ADJUST
PICKUP PASSAGE
' ING
FIG. 4d Idle System
High Speed (Main Metering) System
When the throttle plate is advanced to a point just above the idle
range, the suction on the idle system diminishes, but the increased
volume of air entering the engine through the venturi creates
sufficient vacuum (suction) on the discharge jet to draw a mixture
of fuel and air from the metering well. With the float chamber
vented to air intake pressure, the pressure in the float chamber
causes fuel to flow from the fuel bowl through the main jet into the
metering well and discharge jet where it is mixed with air taken in
through the well vent jet at a point below the level of fuel in the
main discharge jet. The fuel-air mixture from the main discharge
jet is discharged into the air stream at the throat of the venturi and
mixed with the air passing through the venturi.
:IG. 4e High Speed System
CALIBRATION
WELL \
VEN(URl
DISCHARGE
C
JET