Holley MCarbHoll2110 1957 Carburetor manual
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the flow of fuel. Sufficient fuel to replace the fuel
that is used will then be the only fuel admitted.
Thus, any change in the fuel level, causes a cor
responding movement in the float, opening or
closing the fuel inlet needle valve to immediately
restore the proper fuel level. The specified level
of fuel is maintained because the four basic fuel
metering systems are calibrated to deliver the
proper mixture only when the fuel is at the level.
The Model 2110 Truck Carburetors are equip
ped with a manual choke, the Model 2110-EEC
Passenger Carburetors are equipped with an auto
matic choke. The choke supplies the richer fuel
air mixture required for starting and operating a
cold engine. Most of the vaporized fuel from the
carburetor condenses to a liquid upon contact with
the cold surfaces of the intake manifold. This fuel
in liquid form burns too slowly and incompletely
in the cylinders, causing loss of power and stalling.
The choke plate, which is closed during the warm
up and choking period, confines the manifold vacu
um below the plate. This greater vacuum causes
both the main metering and idle system to dis
charge fuel into cylinders.
Sufficient fuel is
supplied to the cylinders.
The automatic choke is mounted on the air
horn and is linked to the choke shaft. It controls
the air flow into the carburetor.
The bi-metallic thermostat spring in the
choke control mechanism will expand when cold,
loosening and unwinding its coils. When warm, it
will contract, winding the coils tighter. When the
engine is cold, the thermostat spring expands,
holding the choke plate in the closed position.
When the engine is started, manifold vacuum acts
directly on the choke plate, and a vacuum piston
located in the choke housing, immediately moving
against the tension of the thermostat spring
to partially open the choke plate to prevent stalling.
The choke shaft does not pass through the center
of the choke plate. Instead, it is offset, thus ex
posing a much larger area at one side of the closed
choke plate to manifold vacuum. When the engine
is started or at idle, manifold vacuum is not suf
ficiently strong to open the choke plates, but the
impact of air against the choke plate partially opens
the plate.
Manifold vacuum channeled through a passage
in the choke control mechanism acts to draw the
choke vacuum piston downward, thus exerting
another opening force upon the choke plate. These
two features allow enough air to enter the engine
to enable it to run smoothly.
As the engine continues to run, the vacuum
acting on the choke vacuum piston draws air from
under the intake manifold through the heat tube
in the manifold where the air is warmed by the
engine heat, and then through the thermostat
housing where the air warms the thermostat
spring, causing it to contract. This gradually de
creases the tension of the thermostat spring as
manifold temperature rises, permitting the vacu
um acting on the choke vacuum piston to further
open the choke plate. The air then flows through
the manifold vacuum passage in the carburetor
and is exhausted into the air stream in the throttle
When the engine reaches its normal operating
temperature, the thermostat spring no longer ex
erts an opposing tension on the choke vacuum
piston, allowing the vacuum piston to pull the choke
plate to the full open position.
In the full open position the vacuum piston is
in its lowest position in the cylinder. Slots in the
cylinder wall permit sufficient air to bleed past
the piston and into the intake manifold to allow a
continual flow of warm air to pass through the
thermostat housing. This keeps the thermostat
spring warm and the choke plate fully open until
the engine is shut down and allowed to cool.
During the warm-up period, the air flow past
the partially opened offset choke plate acts upon
the plate in much the same manner as manifold
vacuum does upon starting. As air flow increases
with increased engine speed, the engine requires
less choking and the force of the increased air
flow holds the choke plate closer to the open
position. The offset choke plate, vacuum piston,
and thermostat spring are engineered to provide
the correct degree of choking for all conditions
of engine speed, power output, and temperature.
The choke lever at the carburetor actuates a
fast idle cam during choking. 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
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 is reduced.
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