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ENGINE FUEL AND EXHAUST SYSTEMS
STROMBERG CARBURETOR
3-45
Figure 3-69-Stromberg Choke
During Warm-up
step into position for the throttle stop screw.
The engine will then run at a lower speed at
closed
throttle.
See figure 3-69.
VALVE
THERMOSTAT
PISTON
After the engine starts running, intake mani-
fold vacuum causes the piston to partially open
the choke valve against the spring tension of
thermostat, thereby admitting sufficient air to
give a satisfactory running
mixture.
Figure 3-68-Stromberg Choke in Cold Starting Position
When accelerator pedal is released after
starting the engine, the throttle stop screw
comes to rest against a step of fast idle cam
which was rotated to the fast idle position by
the closing of choke. This provides proper
throttle opening to prevent stalling of the cold
engine. See figure 3-68.
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 choke valve will open the valve against the
spring tension of the
thermostat.
These oppos-
ing forces balance the choke valve at a position
which provides the required choke action with-
out causing loading or an excessively rich mix-
ture. At wide open throttle the vacuum piston
does not help to open the choke 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 choke housing by manifold vacuum
operating through
t
he small
slot
in
vacuum
piston and hole in choke
housing.
Th
is
warms
the thermostat, causing it to reduce its spring
tension on choke valve in proportion to the in-
crease in temperature.
When the throttle is opened and throttle stop
screw is lifted from the fast idle cam, the choke
valve then moves to a more open position and
the fast idle cam is rotated to bring a lower
d. Choke Operation-Hot Engine
When the engine reached normal operating
temperature, the choke thermostat is heated to
the point where it no longer exerts any spring
tension on the choke valve. The choke valve is
in the wide open position and the fast idle cam
is in the slow idle position so that the throttle
stop screw bears against the lowest step of fast
idle cam at closed throttle. See figure 3-70.
e.
Choke Unloader Operation
If
the engine becomes
flooded
for any reason,
the choke valve can be partially opened by de-
FAST IDLE ROD MUST
NOT STICK IN SLOT
Figure 3-70-Stromberg Choke in Hot Position
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