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 TM 5-2805-261-13
Figure 1-8. Fuel pump
3.
The diaphragm operated fuel pump is mounted
directly over a port in the crankcase. The
pressure and partial vacuum conditions created
in the upper crankcase act on the diaphragm,
causing it to move back and forth. This back
and forth motion is the pumping action.
Figure 1-6. Carburetor (2 of 2)
Two one-way valves in the pump control the direction of fuel
flow so that it moves only toward the carburetor.
The slow speed needle valve operates when the engine is at idle
PARTIAL VACUUM IN POWERHEAD
and slow speeds. The throttle valve is closed and reduces the
air flow into the carburetor. This cuts off the flow of fuel from
the high speed nozzle. An adjustable flow of fuel is allowed to
enter the slow speed reservoir, mix with a small amount of air,
and go to the crankcase.
2.
There are two leaf valves on the unit, one for
each piston and crankcase compartment.
As piston movement creates alternating conditions of pressure
and partial vacuum in each compartment, the leaf valves open
and close. They open when there is partial vacuum in a
crankcase compartment, and close when there is back
pressure. This allows the fuel-air mixture to enter the crankcase
and prevents it from backing out into the carburetor throat.
Figure 1-9. Operation of fuel pump
Figure 1-7. Leaf valves
1-7
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