Suzuki 2005 GSF1200 Service Manual page 166

1G-4 Fuel 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 "B" is admitted into the diaphragm chamber (2) through an orifice "C" provided in the
piston valve (1).
Rising negative pressure overcomes the spring (3) 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.
[A]
1. Piston valve
2. Diaphragm chamber
2
3
"C"
1
"A"
"B"
3. Spring
"A": Venturi
[B]
"B": Negative pressure
"C": Orifice
I649G1170004-03
[A]: Lower position of piston valve
[B]: Upper position of piston valve