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S. ACCELERATING PUMP SYSTEM
As the throttle opening is increased
upon
acceleration, the air flow through
the carburetor
responds almost immediately. There
is, however,
a brief interval before the fuel,
which is heavier
than the air, can gain speed and
maintain the de
sired balance of fuel and air. It
is during this
interval that the accelerating pump
operates,
supplying fuel until the other systems
can provide
the proper mixture.
The accelerating pump is connected
by the
pump link to the throttle lever
and is actuated by
throttle movement. When the throttle
is closed,
the pump piston moves upward, drawing
fuel from
the float chamber through the pump
inlet and into
the pump chamber. The pump inlet
check valve
opens to permit fuel to enter the
pump chamber,
and closes to prevent a reverse
flow of fuel when
the pump is operated. When the throttle
is opened,
the pump piston moves downward,
forcing fuel
through the pump discharge passage
to raise the
pump discharge needle. The fuel
then flows around
the pump discharge needle and out
of the pump dis
charge nozzle into the air stream
entering the
venturi. A slot in the pump piston
stem allows
the pump operating rod to overrun
the pump piston
stem, compressing the pump spring
when the throt
tle is opened suddenly. This overrun
causes the
pump piston to be subjected to the
pressure of the
compressed pump spring, thereby
giving a pro
longed discharge of accelerating
fuel.
A larger or smaller accelerating
pump dis
charge can be obtained by varying
the position of
the pump link in the holes in the
throttle lever.
AUTOMATIC CHOKE SYSTEM
6. AUTOMATIC CHOKE SYSTEM
On the Lincoln and Mercury passenger
car
carburetors, the richer mixture
required for
starting and operating a cold engine
is supplied
through the use of an automatic
choke. Much of
the atomized fuel from the carburetor
condenses
to a liquid upon contact with the
cold surfaces of
the intake manifold. The fuel in
this liquid form
burns too slowly and incompletely
in the cylinders,
causing loss of power and stalling.
The choke is
a method of enriching the fuel discharge
so that
enough vaporized fuel reaches the
cylinders to
permit the engine to run smoothly
during the warm
up period
Operating qualities of the automatic
choke
system for this carburetor have
been improved
by mounting the thermostatic choke
control mech
anism directly on the intake manifold.
The choke
shaft in the carburetor is linked
to the choke mech
anism with a choke control rod.
This type of
