3-23
FUEL SYSTEM
3-23
MODEL 4160 CARBURETOR SYSTEMS (Continued)
MAIN METERING SYSTEM (PRIMARY)
The main metering system on both models
discussed in this section are very similar.
At higher speeds the vacuum is increased at
the main discharge nozzle in the center of the
booster venturi.
This vacuum or pressure differential causes
fuel to flow through the main metering jet into
the main well. The fuel moves up the main well
past one or more air bleed holes from the main
airwell. These air bleed holes are supplied with
the filtered air from the “high speed” air bleeds
in the air horn. The mixture of fuel and air moves
up the main well and through a channel to the
main discharge nozzle in the booster venturi.
Many booster venturi have tabs or projections
which assist
in
providing unique distribution of
the air-fuel mixture in the intake manifold as re-
quired for certain engines.
The booster venturi in this series of car-
buretors are not replaceable, although many
carburetors use separate booster castings that
are permanently installed in the main body
casting.
BOOSTER
GE
E
AIR BLEED
POWER ENRICHMENT SYSTEM (PRIMARY)
During high speed or heavy load operation,
when manifold vacuum is low, the power system
provides added fuel for power operation. A vac-
uum passage in the throttle body transmits vac-
uum to the power valve vacuum chamber in the
main body. All of the power valves used in this
series of carburetors are actuated by a vacuum
diaphragm. Manifold vacuum is applied to the
vacuum side of the diaphragm to hold it closed
at idle and normal moderate load conditions.
POWER VALVE
When manifold vacuum drops below the
power valve’s calibration, the power valve spring
opens the valve to admit additional fuel. This
fuel is metered by the power valve channel re-
strictions in the metering body. The fuel flows
through the restrictions into the main well and is
added to the fuel flowing from the main metering
.
jets .
N P602A
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