Cummins/Onan 2.5MAJ-3R Engine

1. Turn adjusting screws in gently to seats. Do not force them.
2. Back main screw out about 2-1/2 full turns (1-1/2 on downdraft carburetor).
3. Start set and allow it to thoroughly warm up under full-load condition.
4. Slowly turn main adjusting screw inward (clockwise) for leaner mixture until set loses speed or voltage drops.
5. Turn screw outward (counterclockwise) until set carries full load.
6. Check operation at various loads.
7. If hunting, turn adjusting screw out for richer mixture, not more than 1/2 turn beyond maximum generator output.
8. For AC sets, adjust idle screw with no AC load connected.
9. For battery charging sets, adjust idle screw at lowest possible charge rate.
10. Slowly turn idle adjusting screw inward until set loses speed; then outward until set runs smoothly.
11. Adjust throttle idle stop screw to clear throttle shaft stop by 1/32 inch.

Tools: voltmeter, tachometer

1. Connect voltmeter across generator output.
2. With no electrical load, start set and adjust speed adjusting nut to approximately 126 volts maximum for a 120-volt set.
3. Apply full rated electrical load; voltage should be approximately 108 volts or higher.
4. For 240-volt plants, 252 volts at no-load is maximum and 216 volts full-load is minimum.
5. If voltage spread is too great, move governor speed spring end closer to governor shaft.
6. Test governor action at various load conditions.
7. If hunting, turn sensitivity stud slightly outward; any change requires speed readjustment.
8. If using tachometer, full-load speed for 60 cycle 4-pole is 1800 rpm, 2-pole is 3600 rpm; spread not more than 100 rpm (1800) or 200 rpm (3600).

1. Turn knurled speed adjusting nut (spring tension nut) to give desired charge rate.
2. If governor hunts, turn sensitivity adjusting stud outward to move spring end farther from governor shaft center.
3. Any change in sensitivity requires compensating change in speed adjustment.
4. Maximum speed at full load operation is approximately 2400 rpm.

Tools: 7/16 inch wrench, 9/16 inch wrench

1. Remove valve compartment cover.
2. Crank engine over by hand until intake valve (nearest carburetor) opens and closes.
3. Continue turning flywheel slowly until mark on flywheel aligns with TC mark on gear cover.
4. Correct tappet clearance for both intake and exhaust valves is in Dimensions and Clearances.
5. Use a 7/16 inch wrench for the screw and a 9/16 inch wrench for the tappet when making any adjustment.

1. Check point gap is properly adjusted.
2. Install flywheel loosely with its key in place.
3. Turn flywheel in rotation direction to position where mark on flywheel aligns with proper degree on gear cover.
4. Points should just separate at this point.
5. If not, remove flywheel and loosen magneto backplate mounting screws slightly.
6. If points separate too soon, shift entire backplate assembly clockwise.
7. Tighten backplate mounting screws and recheck work for accuracy.
8. When replacing flywheel, ensure key is properly in place on crankshaft.

Tools: voltmeter

1. Remove relay from circuit.
2. Place 12 volts on one side of relay coil and ground the other side. If relay activates it is operating.
3. Place a 12 volt source to one side of the contacts.
4. Place voltmeter to other side of relay contact and to ground. If 12 volts present when relay energized, relay is good.
5. If relay has more than one set of contacts, each set must be checked in this fashion.

Tools: ohmmeter

1. Remove battery B+ cable.
2. Disconnect one side of resistor and using an ohmmeter measure across resistor for an accurate reading.

1. Remove solenoid from circuit.
2. Apply 12 volts to terminal marked Battery.
3. Jumper a ground wire to terminal marked S on start solenoid.
4. Solenoid should activate.
5. If solenoid is good, 12 volts can be read between S and ground.

Tools: ohmmeter

1. Remove B+ cable.
2. Place ohmmeter leads across switch.
3. Activate switch. If a short is read on meter, switch is good.

Tools: thermometer, pan

1. Remove thermostat from cylinder head.
2. Heat a pan of water to approximately 150°F.
3. Suspend thermostat in hot water so sensitive portion does not touch pan.
4. Bring water temperature to 155° to 165°F; thermostat should start to open within this range.
5. When completely open, lift out into air; thermostat should close within a short time.
6. If thermostat does not operate properly, replace with a new one.
7. Install new gasket when replacing thermostat.

1. Install new commutator brushes when old ones are worn to 5/8 inch or less in length.
2. Collector ring brush may be used until worn to 5/16 inch in length.
3. Remove end cover to expose brush rig; brushes and leads are accessible.
4. New brushes are shaped to fit and seldom need sanding to seat properly.
5. Always use the correct brush as listed in the parts list; never substitute.
6. Be sure to tighten brush lead terminal nuts.
7. If brush sparking occurs after replacement, run set at light load until brushes wear to a good seat.

Tools: solvent

1. Every 100 hours or sooner, remove breather tube.
2. Wash valve (5/16 inch ball) in a solvent.
3. Check breather tube for security and leaks.