Buick LeSabre 1965 Service Manual page 127

ENGINE FUEL AND EXHAUST
4-BARREL CARTER 3 - 5 1
best possible seating action of
the intake needles.
Intake needles and seats are
carefully matched during manu-
facture. Do not use the left needle
in the right seat or vice versa.
To avoid unnecessary bending,
both floats should be reinstalled
in their original positions and
then adjusted.
The bowls are vented to the inside
of the air horn and also to atmos-
phere. A connecting vent passage
in the air horn effects a balance
of the air pressure between the
two bowls. Bowl vents are cali-
brated to provide proper air pres-
sure above the fuel at all times.
c. Operation of Low
Speed Systems
F u e l for i d l e and early part
t h r o t t l e operation is metered
through the low speed system.
The low speed system is located
on the primary side only. See
Figure 3-65.
Gasoline enters the idle wells
through the main metering jets.
The low speed jets measure the
amount of fuel for idle and early
part throttle operation. The air
by-pass p a s s a g e economizers
and idle air bleeds are carefully
calibrated and serve to break up
the liquid fuel and mix it with air
ECONOMIZER
MAIN 1
METERING
JET
IDLE ADJUSTING
SCREW PORT
LOW-SPEED JET
AIR PASSAGE
TO OUTLET BELOW
THROTTLE VALVES
Figure 3-65—Low Speed Circuit
Figure 3-66—Thermostat?c
Valve Assembly
as it moves through the passages
to the idle ports and idle adjust-
ment screw ports. Turning the
idle adjustment s c r e w s toward
their seats reduces the quantity of
fuel mixture supplied by the idle
circuit.
The idle ports are slot shaped.
As the throttle valves are opened,
more of the idle ports are un-
covered allowing a greater quan-
tity of the gasoline and a i r
mixture to enter the carburetor
bores. The secondary throttle
valves remain seated at idle.
The low speed jets, air bleed,
economizer and by-pass bushings
are pressed in place in the ven-
turi assemblies. Do not remove
in servicing. If replacement is
necessary, use a new venturi as-
sembly. To insure proper align-
ment of the low speed mixture
passage, each primary venturi
assembly is designed so it can be
installed on one side only.
To assist in quick hot engine
starting, fuel vapor accumulated
in the primary and secondary
bores is vented to atmosphere
through v e n t passages a b o v e
throttle valves.
To combat engine stalling during
warm-up on cool humid d a y s ,
caused by "carburetor icing",
e x h a u s t gases a r e directed
against a steel baffle plate that
contacts the carburetor mounting
flange. The heat transferred helps
eliminate ice formation at the
throttle valve edges and idle
ports.
To compensate for loss of engine
RPM while idling under very hot
operating conditions, a thermo-
static valve assembly is installed
in the web between the right and
left secondary venturi. When the
temperature rises beyond a cer-
tain point, the calibrated thermo-
static s p r i n g opens the valve.
This allows additional air to flow
through a special passage to an
outlet below the secondary throt-
tle valves. At normal operating
temperatures, the valve should
be closed. The thermostatic valve
cannot be adjusted or repaired;
therefore, a faulty valve must be
replaced. See Figure 3-66.
d. Operation of High
Speed Systems
Fuel for all except early part
throttle and for all full throttle
operation is supplied through the
high speed system. See Figure
3-67.
STEP-UP PISTON
AND SPRING
ATMOSPHERIC
VENT PASSAGE
TC STEP-UP
PISTON
NTI-PERCOLATO
D HIGH SPEED
AIR BLEED TUBE
MAIN VENT
TUBE
VACUUM
PASSAGE
Figure 3-67—Primary High
Speed Circuit