Buick LeSabre 1965 Service Manual page 130

3 - 5 4 4-BARREL CARTER ENGINE FUEL AND EXHAUST
thermostatic coil loses its ten-
sion gradually, until the choke
valve r e a c h e s the full-open
position.
If the engine is accelerated during
the warm-up period, the corre-
sponding drop in manifold vacuum
allows the thermostatic coil to
m o m e n t a r i l y partially close
the choke, p r o v i d i n g a richer
mixture.
During the warm-up period, it is
necessary to provide a fast idle
speed to prevent engine stalling.
This is accomplished by a fast
idle cam connected to the choke
linkage. The fast idle adjusting
screw on the t h r o t t l e lever
contacts the fast idle cam and
prevents the throttle valves from
returning to a normal warm en-
gine idle p o s i t i o n , while the
choke is in operation. See Fig-
ure 3-71.
If during the starting period the
engine becomes flooded, the choke
valve may be opened manually to
clean out excessive fuel in the
intake manifold. This is accom-
plished by depressing the ac-
celerator pedal to the floor mat.
The unloader projection on the
throttle lever contacts the fast
idle cam which rotates and par-
tially opens the choke valve.
The secondary section does not
have a choke valve. In order to
prevent air entering the carbu-
retor through the secondary side
during the e n g i n e warm-up
period, it is necessary to lock
FAST I D I f l D l
F A S T I D L E 5 J >
CAM "^»
LEFT
SIDE
V FAST IDLE
SCREW
RIGHT
• I CHOKE
n
R O D
feBj^SJON
UlTCHOKE
PISTON
Figure 3-71—Choke Linkage
the secondary throttle valves in
the closed position. This is ac-
complished by engagement of a
lock-out arm with a locking tang
on the secondary v a l v e shaft
lever. See Figure 3-71.
With the choke valve in wide open
position the lock-out arm rests
in a lowered position, clear of the
secondary valve shaft lever. As
the choke valve closes it rotates
the fast idle cam trip lever, al-
lowing the lock-out arm to rise.
As soon as the choke valve is
closed a few degrees from wide
open position, the notch in the
lock-out arm lies in the line of
travel of the locking tang on
the secondary valve shaft lever,
thereby preventing the shaft and
valves from turning.
The choke fast idle linkage per-
mits the choke valve to float in
that it can close a few degrees,
if necessary, should the engine
falter while running on fast idle
during the warm-up period. When
the e n g i n e starts, manifold
vacuum applied to the choke pis-
ton pulls the choke valve partially
open. Should the engine falter,
the choke piston will sense the
condition because of the reduc-
tion in vacuum and allow the
tension of the thermostatic coil
to partially close the choke, pro-
viding a slightly richer mixture
to smooth out the engine's per-
formance. This feature of al-
lowing the choke valve to close
partially while the fast idle screw
is in contact with the cam helps
prevent stalling during the warm-
up period. The choke valve is
allowed to come open during the
warm-up period if the car is left
running on fast idle while warm-
ing up.
3 - 2 3 DISASSEMBLY,
CLEANING
INSPECTION OF
CARTER 4-BARREL
CARBURETOR
1. Remove pin spring from upper
end of choke rod and disconnect
I COVER
i T
L A T E
RETAINER
SPRING
PISTON
STEP-UP
ROD
SPRING
Figure 3-72—Step-Up Rod and
Related Parts
rod from choke shaft lever. Re-
install pin spring on choke rod
for safe keeping.
2. Remove retainer and spring
from upper end of pump rod and
disconnect rod from pump arm.
Reinstall spring and retainer on
pump rod.
3. Remove screws holding two
step-up piston cover plates to
air horn. Remove cover plates
and remove each step-up piston,
rod, and rod retainer spring as
an assembly. Then remove two
step-up piston springs. See Fig-
ure 3-72.
4. Remove screw from end of
choke shaft and remove outer
lever and washer. Then remove
inner lever and fast idle rod from
carburetor as an assembly. Re-
move choke valve attaching
screws. Remove choke valve and
shaft.
5. Remove fuel inlet fitting and
gasket. Remove all air horn
screws and lock washers, noting
location of attached cable clip.
Remove air horn and gasket from
main body, lifting straight up to
avoid damaging floats or pump
plunger.
6. Remove float lever pins and
floats. Remove float needles,
needle seats, and gaskets. Keep
float system parts separated so
that they may be reinstalled in
original location with a minimum
amount of adjusting.