Suzuki 2005 GSF1200 Service Manual page 165

Fuel Valve
When the engine is not operating, the fuel valve (1) is kept closed by the tension of the spring (2), which closes the fuel
passageway and stops the flow of fuel to the carburetors.
When the engine has started, negative pressure (vacuum) "A" is generated in the combustion chamber and reaches
the diaphragm through a passage in the carburetor's main bore and the vacuum hose. This negative pressure
(vacuum) "A" is higher than the spring pressure which causes the diaphragm to force open the fuel valve (1) and allow
fuel "B" to flow to the carburetor assembly.
[A]
1
2
1. Fuel valve "A": Vacuum
2. Spring "B": Fuel
[B]
[A]: "Fuel stop" condition
[B]: "Fuel flow" condition
Fuel System: 1G-3
"A"
"B"
I649G1170003-02