Onan NHC Series Operator's/Service Manual And Parts Catalog page 163

Complete Replacement: Complete replacement of the.
carburetor should be performed as follows:
1. Follow the previously given disassembly instruc-
tions as required for removal of the defective
carburetor.
2. Replace the carburetor with a new unit, using
attaching parts in good condition and making a l l
the connections previously disengaged.
3. Adjust the needle settings as described under
Adjustments.
FUEL PUMP
The engine uses a diaphragm-type fuel pump. If fuel
does not reach the carburetor, check the fuel pump
before dismantling i t .
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 (he fuel flow
into a container so gasoline does
W A R N I N G
3.
not spill on ignition wires.
If there is enough fuel in the tank, and line does
not have fuel flowing, the pump needs 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 o i l may also
indicate a faulty pump.
NOTE: Always return the hand priming lever all the way
inward so that lever does not prevent normal operation
of fuel pump.
Fuel Pump Reconditioning: Reconditioning of the fuel
pump should be as follows, referring to Figure 14.
1. Remove the fuel lines and mounting screws holding
the pump to the engine.
2. Make an indicating mark with a f i l e 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 i t , 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 dia-
phragm. Press down on the diaphragm to compress
the spring and turn it 90 degrees. This w i l l recon-
nect the diaphragm..
10. Hold the bracket, place the pump cover on i t
(making sure the indicating f i l e 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.
11. Mount the fuel pump on the engine, using new
mounting gaskets. Connect the fuel lines.
U P P E R P U M P BODY
( N O T S E R V I C E A B L E )
• L O W E R S I D E
D I A P H R A G M G A S K E T
P R I M I N G
L E V E R
L O W E R
B O D Y
• P A R T S I N C L U D E D
IN R E P A I R K I T
F I G U R E 14. F U E L P U M P
THERMO-MAGNETIC CHOKE (Optional)
This choke uses a strip heating element and a heat
sensitive bimetal spring to control the choke plate
position. In addition to this, a solenoid is actuated
during engine cranking, closing the choke a l l or part
way, depending on ambient temperature. The bimetal
is factory set to position the choke to the proper
opening under any ambient condition.
17