EMISSION CONTROLS AND FUEL SYSTEM 167
was modified to the extent that a choke pis-
ton was added and the choke valve stop was
relocated in the diiuser cone. This allows an
initial choke opening of 10° which increases
to 30° after an initial cold start. The throttle
valve regulates the flow of air into the mani-
fold and is mechanically actuated by the ac-
celerator pedal. The diffuser cone, sus-
pended in the bore of the air meter inlet,
functions as an annular venturi and acceler-
ates the air flow between the cone and the
meter housing. The air meter houses the pre-
viously mentioned components plus the idle
and main venturi signal systems.
The main venturi vacuum signals are gen-
erated at the venturi as the incoming air
rushes over an annular opening formed be-
tween the air meter body and piezometer
ring. They are then transmitted through a
tube to the main control diaphragm in the fuel
meter. The venturi vacuum signal measures
the flow of air into the engine and automati-
cally controls the air/fuel ratio. The one ex-
ception to this is at idle speeds.
Idle air requirements are handled differ-
ently by the fuel injection method. Approxi-
mately 40% of the idle-speed air flow enters
the engine through the nozzle block air con-
nections tapped into the air meter body. Part
of the remaining 60% flows past the throttle
valve which is pre-set against a fixed stop. The
remainder enters through the idle air, by-pass
passage that is controlled by the large, idle-
speed adjusting screw. Idle speed is adjusted
by turning this screw in or out.
Fuel Meter
The fuel meter's float-controlled fuel reser-
voir is basically the same as that found in con-
ventional carburetion. The fuel meter re-
ceives fuel from the regular engine fuel pump.
The incoming fuel is routed through a 10 mi-
cron filter before entering the main reservoir
of the fuel meter, where the high pressure
gear pump picks it up. This, high pressure,
spur-gear type pump is completely sub-
merged in the lower part of the fuel meter
main reservoir. A distributor-powered, flexi-
ble shaft drives the pump at
Yz
engine speed.
Fuel pressures span a range of near zero to
200 psi, according to engine speed. Fuel not
used by the engine reenters the fuel meter
through a fuel control system. The 1965 fuel
meter contains a vent screen and baffle which
helps to stabilize the air/fuel mixture.
Fuel Control System
A fuel control system regulates fuel pressure
(flow) from the fuel pump to the nozzles. This
flow is controlled by the amount of fuel that
is spilled or recirculated from the high pres-
sure pump, through the nozzle block, back to
the fuel meter spill ports. This is accom-
plished by a three-piece spill plunger or disc
that is located between the gear pump and
the nozzles.
When high fuel flow is required, it moves
downward, closing the spill ports to the fuel
meter reservoir and concentrating the flow to
the nozzle circuits. Correspondingly, the spill
plunger or disc must be raised to allow the
spill ports to be exposed when a low fuel flow
is required. This causes the main output of
the gear pump to by-pass the nozzle circuits
and reenter the meter reservoir through the
now-opened spill ports.
The spill plunger is not mechanically con-
trolled by the accelerator pedal. Fuel control
is accomplished by a precisely counterbal-
anced linkage system sensitive to fuel pres-
sure and diaphragm vacuum. Thus the slight-
est change in venturi vacuum signal on the
main control diaphragm will activate the link-
age. One end of the fuel control lever rests
against the spill plunger head while the other
end connects by a link to the main control
diaphragm. The control lever pivots on the
roller end of an arm called the ratio lever.
When the increased vacuum above the dia-
phragm forces the control lever upward, the
lever pivots on the ratio lever's roller and
pushes the spill plunger or disc downward.
This closes the spill ports and steps up fuel
flow to the nozzles. When decreased vacuum
above the diaphragm reverses the pivot ac-
tion, fuel pressure forces the spill plunger
HIGH SIGNAL VACUUM -r)
FUEL
CONTROL
LINK
CONTROL LOW SIGNAL VACUI
LINKAGE COUNTERWEIGHT
PLUNGER MOVES
FUEL CONTROL
UP
LEVER
SPILL INCREASES
Fuel control linkage
CONTROL SIGNAL
FUEL CONTROL VACUUM
DIAPHRAGM ___ , PLUNGER,
_____________ ^ ^ ( ] M O V E D O W N
RATIO ^^ """
L E V E R E T SPILL
'' PLUNGER
INCREASES
PRESSURE
DECREASES
