Cummins/Onan NHC-NHCV Generator Set

1. Ensure ignition and governor are adjusted.
2. Start and warm engine.
3. If engine will not start, close both needle valves gently, then open each 1 to 1-1/2 turns, idle first then main.
4. With no load, turn idle adjustment out until speed drops slightly below normal; turn in until speed returns to normal.
5. Apply full load, turn main adjustment in until speed drops slightly below normal; turn out until speed returns to normal.

1. Perform steps 1 and 2 of Adjustment Under Load.
2. Pull governor mechanism to slow unit to about 400-500 rpm.
3. Set idle adjustment screw for even operation.
4. Release governor to accelerate; adjust main needle outward about 1/4 turn if needed.
5. Set throttle stop screw at desired idle speed.

1. Remove fuel line, air cleaner hose, governor linkage, and choke wires.
2. Remove two carburetor mounting nuts and carburetor.
3. Unscrew float bowl nut and remove main fuel adjustment assembly.
4. Invert carburetor and check float surface nearest gasket is 1/8 ± 1/16 inch from gasket.
5. Bend float tab as required.
6. Reassemble, install, and test.

Tools: Tachometer

1. Run engine about 15 minutes to normal operating temperature.
2. Adjust carburetor main jet for best full load mixture.
3. Adjust carburetor idle needle with no load.
4. Adjust length of governor linkage.
5. Check governor linkage and throttle shaft for binding or excessive looseness.
6. Adjust governor spring tension for nominal no load speed.
7. Check rpm drop between no load and full load and adjust sensitivity.
8. Recheck speed adjustment.
9. Set carburetor throttle stop screw.

Tools: Continuity test lamp

1. Connect continuity test lamp across breaker points.
2. Touch one prod to breaker box terminal with coil lead and other to ground.
3. Turn crankshaft counterclockwise until points close.
4. Slowly turn crankshaft clockwise.
5. Lamp should go out just as points break, indicating ignition at 25° BTC.

Tools: Timing light

1. Connect timing light per manufacturer instructions.
2. Start engine and check timing at idle.
3. Pointer on flywheel should line up with 25° mark on cover.
4. If marks do not line up, readjust point gap.
5. To advance timing, slightly open breaker point gap.
6. To retard timing, slightly close breaker point gap.
7. Recheck timing and point gap.

⚠ Adjust valve clearance only when engine is at ambient temperature.

Tools: Feeler gauge

1. Remove parts to access valve tappets.
2. Remove spark plugs.
3. Turn engine by hand until left intake valve opens and closes and TC mark aligns.
4. Ensure both valves closed and left piston at top of compression stroke.
5. Check clearance with gauge between valve stem and tappet.
6. Adjust with self-locking screw to correct clearance.
7. For right cylinder, turn engine one revolution and repeat.
8. Replace parts and torque manifold bolts.

1. Shut down engine at least one hour; adjust at ambient temperature.
2. Loosen screw securing choke body assembly.
3. Rotate choke body clockwise to richen or counterclockwise to lean.
4. For ambient above 85°F, choke should be fully opened.
5. For ambient below 25°F, choke should be opened 1/4 inch with solenoid not engaged.
6. Tighten choke body screw.

Tools: Flat thickness gauge, Screwdriver

1. Remove breaker box cover.
2. Remove spark plugs for easier rotation.
3. Remove mounting screw A and pull points out to disconnect leads.
4. Replace condenser with new one.
5. Install new points but do not fully tighten screw A.
6. Rotate engine until 25° BTC mark aligns, then another 1/4 turn.
7. Set point gap using screwdriver in notch; gap .020 in.
8. Tighten screw and recheck gap.
9. Check ignition timing.

1. Clean components and repair or replace defective parts.
2. Install throttle shaft and plate with new screws and lock washers.
3. Install choke shaft and plate with new screws and lock washers.
4. Install fuel inlet valve seat and valve.
5. Install float and float pin, adjusting float level.
6. Install bowl ring gasket, bowl, and bowl nut; tighten main jet assembly and back out to 1-1/2 turns.
7. Install idle adjusting screw finger-tight and back out 1 to 1-1/2 turns.
8. Install choke and adjust.
9. Install carburetor and connect fuel inlet, governor, air cleaner hose, and choke wires.
10. Adjust needle settings and check performance.

1. Remove fuel line, air cleaner hose, governor linkage, and choke wires.
2. Remove two carburetor mounting nuts and remove carburetor.
3. Remove main jet assembly and bowl.
4. Remove float pin and float.
5. Lift out fuel inlet valve and unscrew valve seat.
6. Remove idle adjustment needle.
7. Remove throttle plate screws and plate, then pull out throttle shaft.
8. Remove choke plate screws and plate, then pull out choke shaft.

⚠ Do not remove heads when hot. Warpage may occur.

Tools: 1/2 inch socket wrench, Torque wrench

1. Use 1/2 inch socket wrench to remove cylinder head bolts; lift heads off.
2. Clean out carbon deposits without damaging sealing edges.
3. Use new head gaskets and clean head and block surfaces.
4. Place heads in position and torque bolts in sequence: 5 ft-lb, then 10 ft-lb, etc., to 17-19 ft-lb.
5. Recheck torque after engine has run 50 hours.