4-2 FUEL AND LUBRICATION SYSTEM
FUEL SYSTEM
The fuel pump is operated by a vacuum force which is supplied from the carburetor intake pipe. The fuel
sent under pressure by the fuel pump flows into the float chamber when the float of the carburetor has
dropped and the needle valve is open. When the needle valve closes, the pressure of the fuel in the hose
connecting the carburetor and the fuel pump increases, and when the set pressure is reached, the opera-
tion of the fuel pump is stopped by the fuel pressure to prevent excessive supply.
FUEL PUMP
Vacuum pulsations from the carburetor intake pipe are used to operate the pump diaphragm A. When vacuum
is applied to the diaphragm A, fuel is drawn from the tank into the diaphragm’s chamber B. As positive
pressure is applied, the diaphragm backs, pushing the fuel through the outlet to the carburetor.
A series of check valves (1 and 2) is used in the fuel flow route to allow the fuel to move in only one
direction, through the pump body.
To intake pipe
From fuel cock
To carburetor
If the fuel pressure in the chamber of carburetor side is too high,
the return valve 3 is opened so that the fuel pressure is re-
leased to the chamber of fuel cock side.
FUEL
VACUUM
FUEL
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