WM 90 Repair Sub Systems
wc_tx000390gb.fm 75
9.5 Diaphragm-Type Carburetor
See Graphic: wc_gr001919
Ref Description Comment
1 Engine impulse The alternating action of the positive pressure and neg-
ative pressure inside the engine crankcase operates the
fuel pump diaphragm.
2 Fuel pump diaphragm The fuel pump diaphragm undulates in response to the
engine impulse and as a result, it feeds the fuel through
the fuel pump.
3 Fuel inlet The fuel inlet is the opening through which fuel is drawn
from the fuel tank.
4 Inlet valve The inlet valve opens when the diaphragm is submitted
to the action of a negative pressure in response to the
movement of the pump diaphragm and the inlet valve
shuts when it is submitted to a positive pressure.
5 Outlet valve The outlet valve shuts when it is submitted to the action
of a negative pressure and opens when submitted to a
positive pressure.
6 Inlet screen The inlet screen filters the fuel that is drawn from the
fuel tank to the carburetor.
7 Inlet needle valve The inlet needle valve controls the fuel that is fed from
the fuel pump to the metering chamber.
8 Throttle valve The throttle valve controls the volume of air drawn into
the engine, thereby changing the engine speed.
9 Air vent hole The air vent hole is open to the atmosphere, with the
purpose of allowing smooth operation of the metering
diaphragm.
10 Metering diaphragm The metering diaphragm has the function of operating
the metering lever, which is pulled up by the variations in
the negative pressure of the engine.
11 Metering lever The metering lever has the function of opening/closing
the inlet valve by transmitting the movements of the
metering diaphragm to that valve.
12 Metering lever spring The metering lever spring has the function of pushing up
the metering lever, thereby shutting the needle valve
when the engine is stopped and when the metering
chamber is full of fuel.
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