Onan NHC Series Operator's/Service Manual And Parts Catalog page 287

W A R N I N G
DIAPHRAGM FUEL PUMP
Some engines use a diaphragm-type fuel pump,
Figure 16. If fuel does not reach thecarburetor, check
the fuel pump before dismantling it.
1. Disconnect the fuel line at the carburetor.
2. Crank the engine and observe whether fuel
comes from the line at the carburetor.
Be sure to direct the fuel flow into a
container so gasoline does not spill on
ignition wires.
3. If there is enough fuel in the tank, and line does
not have fuel flowing, the pump heeds replacing.
Pump failure is usually caused by a leaking
diaphragm, valve or valve gasket, a weak or broken
spring or wear in the drive linkage. Gasoline diluted
oil may also indicate a faulty pump.
Always return the hand priming lever ail the way inward so that
lever does not prevent normal operation of fuel pump.
UPPER PUMP BODY
(NOT SERVICEABLE)
• V A L V E 0 >
GASKET - O ^ p
• V A L V E .
AND CAGE
• L O W E R S I D E
D I A P H R A G M G A S K E T
PRIMING
L E V E R
LOWER
BODY
•PARTS INCLUDED
IN REPAIR KIT
1 1
2. Make an indicating mark with a file across a point
at the union of the fuel pump bolt and cover.
Remove the assembly screws and the upper
pump body.
3. Turn the pump body over and remove the valve
plate screw and washer. Remove the valve
retainer, valves, valve springs, and valve gasket,
noting their position. Discard the valve springs,
valves and valve retainer gasket.
4. Clean the pump body thoroughly with a solvent
and a fine wire brush.
5. Holding the pump cover with the diaphragm
surface up, place the new valve gasket in the
cavity. Assemble the valves in the cavity.
Reassemble valve retainer. Lock in position by
inserting and tightening the fuel pump retainer
screw.
6. Place the pump body assembly in a clean work
area and rebuild the lower diaphragm section.
7. Holding the mounting bracket, press down on the
diaphragm to compress the spring under it,.then
turn the bracket 90 degrees to unhook the
diaphragm so it can be removed.
8. Clean the mounting bracket with a solvent and a
fine wire brush.
9. Replace the diaphragm operating spring, stand
the new spring in the casting, and position the
diaphragm. Press down on the diaphragm to
compress the spring and turn it 90 degrees. This
will reconnect the diaphragm.
Hold the bracket, place the pump cover on it
(making sure the indicating file marks are in line)
and insert the four attaching screws but do not
tighten. With the hand on the mounting bracket
only, push the pump lever to the limit of its travel
and hold in this position while then tightening the
four screws. This is important to prevent
stretching the diaphragm.
Mount the fuel pump on the engine, using new
mounting gaskets. Connect the fuel lines.
10.
PULSATING DIAPHRAGM FUEL PUMP
Pulsating diaphragm fuel pumps (Figure 17) use a
combination of crankcase and spring pressure to
work a diaphragm thus pumping fuel. This pump may
be mounted on the engine rear housing on NHCV
models and on the upper right hand corner of the
blower housing on NHC models. See Figure 17.
FIGURE 16. DIAPHRAGM FUEL PUMP
Fuel Pump Reconditioning: Reconditioning of the
fuel pump should be as follows, referring to Figure 16.
1. Remove the fuel lines and mounting screws
holding the pump to the engine.
On the downstroke of the engine piston, when the
crankcase pressure is greatest, the pump diaphragm
is forced back against the diaphragm spring com-
pressing it and drawing fuel into the pump intake
chamber. The fuel then passes through the intake
reed valve into the output chamber side of the pump.
On the compression stroke, when crankcase pressure
is the lowest, the diaphragm spring forces the
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