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3-30
CARTER CARBURETOR
ENGINE FUEL AND EXHAUST SYSTEMS
(104)
nector rod which connects a lever on the choke
shaft to a fast idle cam mounted on carburetor
body flange. An upper heat pipe connects the
choke housing to a lower heat pipe in the ex-
haust manifold.
Fig. 3-37-Carter Climatic Control
The choker valve is mounted off-center on
the choke shaft so that the force of air stream
passing through the air horn tends to move
the valve to the open position. A short lever
riveted to choke shaft is engaged by the free
outer end of the thermostatic coil which, when
cold, tends to close the choker valve. The choke
piston, which is actuated by intake manifold
vacuum, is connected by a link to the short
lever on choke shaft and tends to open the
choker valve when the engine is
running.
See
figure 3-37.
The lower heat pipe
in
the exhaust manifold
heats the air which is drawn through it and the
upper heat pipe into the thermostatic coil hous-
ing. Two slots in t
he
choke piston cylinder per-
mit manifold
vacuum
to draw this heated air
through the thermostatic coil housing and down
into the manifold. A baffle plate separates the
thermostatic housing from the housing
on
air
horn to insure
circulation
of
heated
air around
the thermostatic coil.
The fast idle cam trip lever is connected by
a rod to a choker lever on the outer end of
choke shaft so that the fast idle cam is rotated
as the choker valve moves. In closed throttle
position when choker
valve
is not wide open
,
a fast idle adjustment screw on throttle shaft
lever bears against the edge of the fast
idle
cam to give a greater throttle opening than
that provided by the throttle lever adjustment
screw.
The edge of the cam is graduated in
height from center to give increased throttle
opening as choker valve moves toward closed
position. When choker valve is in wide open
position, the fast idle adjustment screw is op-
posite an opening in edge of cam so that throt-
tle may close against the throttle lever adjust-
ment screw.
b. Choke Operation-Cold Engine
When the engine becomes cold the thermo-
static coil also becomes cold and increases its
spring tension sufficiently to close the choker
valve. It is prevented from closing the valve,
however, because the fast idle adjustment screw
holds the fast idle cam in the slow idle posi-
tion;
consequently,
the choker valve is held par-
tially open.
When the accelerator pedal is depressed to
start the engine, the fast
idle
adjustment screw
is lifted clear of the fast idle cam and the
thermostatic coil then closes the choker valve.
After the engine starts running, intake mani-
fold vacuum causes the piston to partially open
the choker valve against the spring tension of
thermostatic coil, thereby admitting sufficient
air to give a satisfactory running
mixture.
·
When accelerator
pedal
is released after
starting the engine, the fast idle adjustment
screw comes to rest against a
high
point of
fast idle cam which was rotated to the fast idle
position by the closing of choker valve. This pro-
vides proper throttle opening to prevent stall-
ing of the cold engine.
If
the throttle is partially opened while the
running engine is cold, the vacuum piston and
the increased force of air flow against the off-
set choker valve will open the valve against the
spring tension of the thermostatic coil. These
opposing forces balance the choker valve at a
position which provides the required choke ac-
tion without causing loading or an excessively
rich
mixture.
At wide open throttle the vacuum
piston does not help to open the choker valve.
c. Choke Operation-Warm-Up
Period
.
As
the engine and exhaust manifold warm
up, warm air is drawn through the heat pipes
into the thermostat housing by manifold vac-
uum operating through the
slots
in choke pis-
ton
cylinder.
This warms the thermostatic coil,
causing it to r
edu ce
its spring t
ension
on choker
valve in proportion t
o
the in
crease
in tempera-
ture. The choke piston moves the choker valve
to a more open position within the range per-
mitted by the fast idle cam trip lever, which
can move independently of the fast idle cam
which is held stationary at closed throttle by
the fast idle adjustment screw.
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