Cummins/Onan YK Engine

⚠ Never change factory settings of the regulator springs or contact fingers.

Tools: dc voltmeter, screwdriver

1. Snap toggle switch to RHEOSTAT ON position.
2. Adjust manual rheostat for 70 volts exciter voltage across dc brushes A1 and A2.
3. Shift brush rig to position giving the highest voltage (neutral).
4. Adjust manual rheostat to obtain rated AC voltage.
5. Snap toggle switch to REGULATOR ON position.
6. Set regulator rheostat at approximately middle of rotation.
7. Set adjustable resistor to obtain rated AC voltage; retighten clip.

⚠ A soap bubble over the regulator outlet will not accurately test for regulator closing.

Tools: manometer

1. Connect a manometer reading up to 14 inches water column to the regulator test hole near the inlet; turn gas on.
2. Turn closing adjusting screw (G) inward just until manometer reading remains constant when outlet is repeatedly covered and uncovered.
3. Close gas supply valve, remove manometer, bleed air from line, install test-hole plug, open valve.
4. Secure hose between regulator nipple and carburetor inlet with clamps.
5. Operate engine to assure quick starting.

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.

⚠ Be sure all load is removed when adjusting the bumper screw.

Tools: tachometer or frequency meter

1. With engine stopped and tension on governor spring, adjust linkage so carburetor stop lever clears stop boss by not less than 1/64 in.
2. Start plant and allow it to reach operating temperature.
3. With no load, adjust speed screw to proper no-load speed.
4. Apply full rated load at 0.8 power factor and recheck speed.
5. If hunting under load, slightly increase distance between governor main shaft and sensitivity screw.
6. If hunting at no load, screw in bumper spring screw until hunt stops.
7. Tighten all lock nuts.

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.

1. An adjustable resistor in series with the line contactor coil adjusts the contactor pull-in voltage.
2. Do not adjust this resistor unless the line contactor will not pull in when the generator set starts.
3. Or if it pulls in at too low a voltage causing the generator set to cycle.

⚠ This is the only adjustment permitted on the regulator plug-in unit.

Tools: screwdriver

1. Remove the louvered cover from the regulator box.
2. Remove the clamping bar from the metal cover of the plug-in unit.
3. Remove the cover held by two screws at the top.
4. Turn the slotted screw at the center until the hunting just stops.

Tools: Phillips screwdriver

1. If the demand control will not keep the generator set running with the minimum load, adjust the variable resistor on the terminal board.
2. Turn the adjustment screw with a Phillips screwdriver counterclockwise to decrease load required for operation.