5
INTERMEDIATE OPERATION
Fuel is delivered into and through the carburetor in the same manner as when the engine is idling.
However, as the throttle opens and engine speed increases, more fuel is demanded from the carburetor
and supplied to the engine by valving in the secondary idle discharge port located immediately behind
the throttle shutter.
As the throttle shutter continues to open and engine speed increases, the velocity of air through the
venturi creates a low-pressure area at the venturi throat and diminishes the suction on engine side of
the throttle shutter. When the pressure at the venturi throat is less than existing within main diaphragm
fuel chamber, fuel is drawn up through main fuel adjustment orifice and out main fuel discharge port into
air stream entering engine intake.
HIGH SPEED OPERATION
As the throttle shutter progressively opens from intermediate position to full open position, the air
velocity through the venturi increases and fuel is metered up through main fuel adjustment orifice and
main fuel discharge port in accordance with the power requirements of the engine. The action of the
main diaphragm is the same as previously described with suction required to operate the diaphragm
being transmitted through the main fuel discharge port.
SUPPLY FUEL
ATMOSPHERIC AIR
PUMP IMPULSE AIR FUEL UNDER VACUUM
FUEL UNDER PRESSURE
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