4-10 FUEL AND LUBRICATION SYSTEM
DIAPHRAGM AND PISTON OPERATION
The carburetor is a variable-venturi type, whose venturi cross sectional area is increased or decreased
automatically by the piston valve 1. The piston valve moves according to the negative pressure present on
the downstream side of the venturi A. Negative pressure is admitted into the diaphragm chamber 2 through
an orifice 3 provided in the piston valve 1. Rising negative pressure overcomes the spring 4 force, causing
the piston valve 1 to rise into the diaphragm chamber and prevent the air velocity from increasing. Thus, air
velocity in the venturi passage is kept relatively constant for improved fuel atomization and the precise air/fuel
mixture.
LOWER POSITION OF THE PISTON VALVE
UPPER POSITION OF THE PISTON VALVE
NEGATIVE PRESSURE
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