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(217)
around the choke plate to enable
the engine to operate and prevent
flooding.
As the engine starts to operate,
the choke operating piston is pulled
downward by manifold vacuum. The
piston initial pulldown travel is lim-
ited by a vacuum bypass slot in the
piston cylinder wall (Fig. 7). When
the top of the piston reaches the top
of the vacuum slot, the vacuum pull
becomes ineffective due to air that
bleeds in through the slot in the
piston. The choke plate will then
be pulled open a definite distance,
but no farther. The air from the
choke piston cylinder is exhausted
through a passage in the base of
the carburetor flange, into the left
primary barrel and across the edge
of each primary throttle plate.
As the engine warms up, the ten-
sion of the bimetai, thermostatic-coil
gradually decre,ases as the tempera-
ture of the coolant in the water
jacket rises. This action gradually
allows the choke plate to open.
When the engine reaches its nor-
mal operating temperature, the ther-
mostatic-coil spring exerts tension on
the choke plate, forcing it to the
full-open position.
If the engine is accelerated during
the engine warm-up period, the cor-
responding drop in manifold vac-
uum applied to the choke piston al-
lows the thermostatic coil to momen-
tarily, partially close the choke plate.
This action provides a richer air-
fuel mixture.
UNLOADER
If during the starting period the
engine becomes flooded, the choke
plate max be opened manually to
clean out excessive fuel in the intake
manifold. This is accomplished by
fully depressing the accelerator pedal
and engaging the starter. The un-
Ioader projection on the throttle
lever contacts the unloader lug on
the fast idle cam and in turn par-
tially opens the choke plate.
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 con-
nected to the choke countershaft.
The fast idle adjusting screw on the
throttle lever contacts the fast idle
cam and prevents the throttle plates
from returning to a normal warm
engine idle position while the auto-
matic choke is in operation.
LOW SPEED (IDLE)
FUEL SYSTEM
A low speed system (Fig.
8)
is
PART 10-2-CARTER CARBURETOR
FIG.
5-Fioat Assembly
provided to supply fuel for idle-speed
and early part-throttle operation. Air
bleeds, restrictions, and adjustments
are provided to control and me:ter
the fuel-air mixture. The air flow
required for minimum idle speed
operation is controlled by an idle
COOLANT INLET
PRIMARY
ASSEMBLY
FAST IDLE
10-13
INLET NEEDLE SEAT
FUEL INLET NEEDLE
81957-A
air adjusting screw.
At idle and part throttle operation,
the throttle plates are almost closed.
This produces strong manifold vac-
uum below the throttle plates which
creates a great enough difference in
pressure between the fuel bowls and
COVER
LINK
ROD
SECONDARY
THROTTLE SHAFT
CHOKE
LOCKOUT OF
SECONDARY THROTTLE SHAFT
81958-A
FIG. 6-
Thermostati' Choke Unit and Linkage
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Troubleshooting
