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MAIN METERING SYSTEM
turn, is regulated by the speed and power output
of the engine. The difference between the reduced
pressure, or vacuum, in the venturi and the normal
air pressure in the float chamber causes fuel to
flow through the main metering system.
At cruising speed, the fuel flows from the
float chamber through the main jet, which meas
ures or meters the fuel, into the bottom of the
main well. The fuel moves up the main well and
past the narrow air bleed holes in the side of the
main well tube. Air, which enters the main well
tube from the main well air bleed, is added to the
fuel by these air bleed holes. This mixture of fuel
and air, being lighter than raw fuel, responds faster
to any change in venturi vacuum, and vaporizes
more readily than raw fuel when discharged into
the air stream in the venturi. Additional air from
the aspirating nozzle enters the fuel as it passes
from the top of the main well to the vertical pas
sage leading to the nozzle tube extension. This
mixture of fuel and air is then discharged into the
air stream in the venturi through the drum-like
nozzle tube extension which aids fuel distribution.
The throttle plate controls the amount of the fuel
air mixture admitted to the intake manifold, regu
lating the speed and power output of the engine in
accordance with accelerator pedal movement.
There are identical main metering system pas
sages for both barrels of this dual carburetor
and they function simultaneously as described
above.
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