Diaphragm And Piston Operation - Suzuki GSF650S Service Manual

FUEL SYSTEM 4-11

DIAPHRAGM AND PISTON OPERATION

The carburetor is a variable-venturi type, whose venturi cross sectional area is increased or decreased auto-
matically 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 dia-
phragm 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 PISTON VALVE UPPER POSITION OF PISTON VALVE
NEGATIVE PRESSURE