Designed to increase the idle rpm for smoother
running when the engine is cold, the fast idle cam
has a series of steps on one edge. As the choke
lever is moved through its range of travel from the
closed position to the open position, the fast idle
cam rotates, presenting successive steps to a
throttle stop screw. Each step permits a slower
idle rpm as engine temperature rises and choking
|2. SECONDARY SYSTEM|
|A. FUEL INLET - Fuel is supplied to the
secondary fuel bowl through a connecting tube at
the primary fuel inlet. The secondary fuel bowl is
equipped with a fuel inlet valve assembly which
regulates the flow of fuel into the bowl the same
as the primary fuel bowl.
|Automatic Choke||The secondary fuel inlet system must
maintain a specified level of fuel as the secondary
fuel system is calibrated to deliver the proper
|(2) AUTOMATIC CHOKE - Some car
buretor models have an automatic choke which is
controlled by hot air. The automatic choke is
mounted on the main body or in the exhaust cross
over passage of the intake manifold and is linked
to the choke shaft, which controls the air flow into
|The automatic choke is equipped with a
bi-metallic thermostat spring and a vacuum piston.
The vacuum piston on the 4160 with mechanical
secondarys is located in the main body of the car
buretor. They are connected to the choke shaft by
means of levers and linkage. When the engine is
cold, the bi-metal spring closes the choke plate for
starting. When the engine fires, manifold vacuum
is applied to the choke piston which, with the help
of air flow on the offset choke plate, opens the
choke plate against the tension of the cold bi-metal
spring. These pieces have been engineered to allow
enough air to enter the engine and keep it running.
|While the engine warms-up, hot air is
circulated through the choke housing or through the
exhaust cross over passage of the intake manifold
to warm the bi-metal spring. As the bi-metal spring
gets warm, it will release its tension on the choke
shaft and allow the choke plate to gradually open.
The path for the hot air is from heat in the exhaust
manifold, into the choke housing, through the small
slots in the choke piston, through passages in the
carburetor and then into the intake manifoldfor all
models except the 4160 with mechanical secondarys.
This model has the bi-metal spring mounted in the
exhaust crossover of the intake manifold. The di
vorced choke assembly is serviced as a unit.
|There is a choke lever on the carbure
tor which actuates a fast idle cam during choking.
|Secondary Idle and Transfer System|