Cummins/Onan Spec C Generator Set

Tools: 8 penny nail or 1/8 inch rod

1. Loosen carburetor choke arm on its shaft.
2. Slip choke assembly cover upward to remove it.
3. Insert an 8 penny nail or 1/8 inch rod through aligning holes of solenoid armature and core.
4. Tie armature firmly against core.
5. Set choke valve plate fully closed and tighten choke arm on shaft.
6. Remove alignment nail and untie armature; replace cover.

⚠ Do not turn too far; a few degrees are usually sufficient.

1. If choke does not open as engine warms up, check electric heating element.
2. Loosen choke housing clamp screw.
3. Turn housing slightly counterclockwise for over-choking in cold temperatures.
4. Turn housing slightly clockwise to increase choking in high temperatures.
5. Retighten clamp screw.

⚠ Factory carburetor adjustments should not be disturbed.

Tools: voltmeter

1. Allow engine to thoroughly warm up.
2. Adjust idle with no load: turn idle out until speed or voltage drops slightly, then in to normal.
3. Adjust main with full load: turn main in until speed or voltage drops, then out to normal.
4. For gas carburetor, set idle screw inward to seat; turn main gas screw in until drop, then out to normal.
5. Set lock nut securely.
6. Adjust throttle lever stop screw for 1/32 inch clearance.

Tools: voltmeter, frequency meter

1. Disconnect booster external spring.
2. At no load, adjust speed nut for 60-61 cycles (60 cycle) or 50-51 cycles (50 cycle).
3. Apply full load; adjust sensitivity for maximum 3 cycle spread.
4. Connect booster external spring at no load with no tension.
5. Apply full load; frequency should stabilize 1 to 2 cycles higher than no load.
6. Adjust internal spring tension if rise more than 2 cycles or if frequency drops.

Tools: voltmeter, frequency meter

1. Check throttle stop lever clearance approximately 1/32 inch.
2. Start and run at light load to thoroughly warm up.
3. At no load, turn speed adjusting nut for 60-63 cycles (60 cycle plant) or 50-53 cycles (50 cycle).
4. Apply full load; governor should keep frequency spread within 3 cycles.
5. If spread more than 3 cycles, turn sensitivity screw clockwise half turn and compensate with speed nut.
6. Check performance under various loads.

Tools: hand crank

1. Remove magneto end cap.
2. Adjust breaker points to 0.020 inch gap at full separation.
3. Remove right hand cylinder air cover to expose timing hole.
4. Slowly turn engine until IMP mark centers in timing hole.
5. Listen for sharp click from magneto impulse coupling at the mark.
6. If click is early (fast) or late (slow), loosen magneto mounting screws and turn magneto slightly.
7. Repeat until proper timing is attained.

⚠ Tappets set too close may cause burned or warped valves.

Tools: feeler gauge

1. Remove valve compartment covers.
2. Hand crank engine until tappet being checked is on low point of cam lobe.
3. Check clearance for intake and exhaust valves.
4. Adjust to 0.012 inch cold at room temperature.
5. Reinstall covers.

⚠ Do not reverse the connections.

1. For electric starting, use two 6-volt batteries in series or one 12-volt battery.
2. Connect positive post of one battery to negative post of the second for series 12 volts.
3. Connect remaining battery terminals to proper terminals in generator terminal box.
4. Observe correct polarity; do not reverse connections.
5. Above 90°F continuous operation may require reduced battery specific gravity.

⚠ Do not change setting as gears mesh.

1. Turn flywheel until chisel mark 8-1/2 inches before TC is visible through timing hole.
2. Hold magneto and turn its drive gear clockwise until gear locks.
3. Without changing setting, install magneto to engine so gears mesh.
4. Check timing as previously described.

⚠ Avoid excessive strain on any one mounting foot.

1. Choose concrete or heavy timber base, minimum 20" x 20".
2. Allow approximately 24" clearance on all sides for servicing.
3. Space 3/8 inch mounting bolts 16-1/2" x 16-1/2"; use 16-1/4" front-to-rear for models ending in A.
4. Assemble mounting cushions, washers, and spacer bushings as shown.
5. Keep base smooth and level; avoid excessive strain on mounting feet.

1. Use SPDT momentary contact switch with center OFF.
2. Connect switch common to plant terminal No. 1.
3. Connect another switch terminal to terminal block No. 2 (stopping).
4. Connect remaining switch terminal to terminal block No. 3 (starting).
5. Terminal No. 1 is grounded; B terminal only for line transfer.
6. Additional remote switches must be connected in parallel.

⚠ Consult local electrical code.

1. For 120/240V 3-wire, leave jumpers across M3 and M2.
2. For 120V 2-wire full capacity, remove M3-M2 jumpers; install one across M1-M3 and one across M2-M4.
3. Connect black hot to M1, white ground to M4.
4. For 240V ungrounded, leave jumpers M3-M2 and connect load to M1 and M4.
5. For grounded 240V, follow procedure A if model ends A, procedure B if B/C etc.