Onan B48 Generator Set

⚠ Make sure feeler gauge is clean and free of any grease, oil or dirt.

Tools: Flat feeler gauge, Allen wrench

1. Remove spark plugs.
2. Remove breaker box cover. Rotate crankshaft clockwise (facing flywheel) until points are fully open.
3. Remove condenser (screw A) and detach condenser lead and coil lead (screw B).
4. Remove two Allen screws (C) and lift breaker assembly from engine.
5. Replace condenser and point assembly with new parts and reinstall in reverse order of removal.
6. Rotate crankshaft clockwise by hand until points fully open; set point gap with a clean flat feeler gauge to 0.016 in by adjusting the Allen socket head screw (D).
7. Replace breaker box cover, coil wire, spark plugs, and spark plug cables.

1. Start engine and allow it to warm up thoroughly (at least 10 minutes).
2. Move engine speed control to the slow position.
3. Bend or turn the low speed stop on the governor so the throttle stop screw on the carburetor controls engine speed.
4. Adjust the throttle stop screw for 1000 rpm idle.
5. Adjust the governor low speed stop for 1100 rpm idle.
6. Move engine speed control to the fast position.
7. Bend the high speed stop on the governor so the engine runs at the vehicle manufacturer's recommended speed.

⚠ Overtightening the mixture adjustment screw will cause carburetor damage; turn in only until light tension can be felt.

1. Turn both mixture screws in until lightly seated, then back the idle mixture screw out 1-1/8 turns and the main mixture screw out 1-1/4 turns.
2. Start the engine and allow it to warm up thoroughly (at least 10 minutes).
3. Move the engine speed control to the slow position.
4. Determine if the engine has a governor low speed adjustment screw.
5. Pull the governor back so the throttle stop screw is against its stop and hold the governor arm there.
6. Adjust the throttle stop screw to obtain 1200 RPM without a low speed screw, or 1100 RPM with one.
7. Turn the idle adjustment screw in until speed drops, then out until speed drops again; set about 1/8 turn outward from the midpoint.
8. Engines with a governor low speed adjustment screw: adjust it to obtain 1200 RPM.
9. Check main mixture by rapidly accelerating from idle to full; turn main screw out in 1/8 turn increments if needed, up to 1/2 turn beyond original.

⚠ Overtightening the mixture adjustment screw will cause carburetor damage; turn in only until light tension can be felt.

1. Identify whether the carburetor is the full adjustment or limited idle mixture type.
2. Full adjustment: back idle mixture screw out 3/4 turn; back main mixture screw out 1-1/4 to 1-1/2 turns.
3. Limited idle mixture: idle fuel adjustment is restricted to 1/4 turn by a limiting cap; no main fuel adjustment screw.
4. Start the engine and allow it to warm up thoroughly (at least 10 minutes).
5. Move the engine speed control to the slow position; bend or turn the low speed stop so the throttle stop screw controls speed.
6. Adjust the throttle stop screw for 1000 rpm idle.
7. Full adjustment: set the idle mixture screw about 1/8 turn outward (rich) from the midpoint of the highest-speed range.
8. Readjust the throttle stop screw for 1000 rpm idle, then adjust the governor low speed stop for 1100 rpm idle.
9. Move the speed control to fast; bend the high speed stop so the engine runs at the manufacturer's recommended speed.
10. Check the main mixture by rapidly accelerating from idle to full; adjust in 1/8 turn increments if needed, up to 1/2 turn beyond original.

⚠ Do not adjust when engine is warm

Tools: Feeler gauges, 7/16-inch open end wrench, 9/16-inch open end wrench

1. Remove ignition key to prevent accidental starting
2. Remove all parts necessary to gain access to valve tappets
3. Remove spark plugs to ease turning engine over
4. Turn engine flywheel by hand until left intake valve opens and closes
5. Continue turning until TC mark on flywheel aligns with TC mark on gear cover
6. Insert correct feeler gauge between valve stem and tappet
7. Feeler gauge should pass freely; thicker gauge should not
8. Turn adjusting screw using 7/16-inch wrench to obtain correct clearance
9. Rotate engine one complete revolution and repeat for right cylinder
10. Replace all removed parts and tighten securely

⚠ If timing is early (advanced) the point gap is too large. If timing is late (retarded) the point gap is too small.

Tools: Ohmmeter or continuity test lamp

1. Adjust the breaker points.
2. Remove the blower housing to expose timing marks on top of the gearcase cover and flywheel.
3. Rotate the flywheel clockwise until the timing mark aligns with the 21 degrees BTDC mark on the gearcase cover.
4. Connect an ohmmeter or continuity test lamp across the ignition breaker points; touch one prod to the coil lead terminal (screw B).
5. Touch the other test prod to a good ground on the engine.
6. Turn the crankshaft counterclockwise until the points close, then slowly turn clockwise.
7. The lamp should go out or continuity be lost just as the points break, which is where ignition occurs; adjust point gap accordingly.

Tools: Ohmmeter or continuity test lamp

1. Adjust breaker points.
2. Remove blower housing to expose timing marks on top of gearcase cover and flywheel.
3. Rotate flywheel clockwise until timing mark aligns with the mark corresponding to 16° BTC on top of gearcase cover.
4. Connect an ohmmeter or continuity test lamp across the ignition breaker points; touch one prod to the coil lead terminal.
5. Touch the other test prod to a good ground on the engine.
6. Turn crankshaft counterclockwise until points close, then slowly turn clockwise.
7. Lamp should go out (continuity lost) just as points break. If timing early the gap is too large; if late too small. Adjust accordingly.

⚠ Failure to adequately wring out excess oil may cause a drop in engine horsepower due to increased restriction of inlet air.

1. Wash in water and detergent and squeeze dry like a sponge.
2. Rinse with water and allow to dry.
3. Coat evenly with two tablespoons (28 grams) of SAE 30 engine oil.
4. Knead into and wring out excess oil from the element wrapper.
5. Install over the air cleaner element.

⚠ Failure to adequately wring out excess oil from the wrapper may cause a drop in engine horsepower due to increased inlet air restriction.

1. Service air cleaner element by gently tapping element on a flat surface.
2. Wash element wrapper in water and detergent and squeeze dry like a sponge.
3. Rinse with water, allow to dry.
4. Coat evenly with two tablespoons (28 grams) of SAE 30 engine oil.
5. Knead into and wring out excess oil from element wrapper.
6. Install over air cleaner element.

⚠ Failure to wring out excess oil may reduce engine horsepower

1. Check and clean air cleaner element every 25 hours
2. Clean by gently tapping element on flat surface
3. Replace element every 200 hours
4. For pre-cleaner: wash in water and detergent, squeeze dry
5. Allow to dry, then coat evenly with two tablespoons (28 grams) of SAE 30 engine oil
6. Knead into and wring excess oil from pre-cleaner
7. Reinstall over cartridge

⚠ Do not smoke or allow any ignition source near the battery.

⚠ Do not add water to battery in freezing weather unless the engine is run two or three hours.

Tools: Battery hydrometer

1. Keep the battery clean by wiping it with a damp cloth whenever dirt appears excessive.
2. If corrosion is present, remove cables and wash terminals with an ammonia solution or a solution of 1/4 pound baking soda in 1 quart of water.
3. Ensure vent plugs are tight; flush the outside of the battery and compartment with clear water.
4. Keep terminals clean and tight; coat with a light application of petroleum jelly or non-conductive grease.
5. Use a battery hydrometer to check specific gravity of electrolyte in each cell.
6. Correct reading by adding 0.004 for every 5°F the electrolyte is above 80°F (27°C) or subtracting 0.004 for every 5°F below.
7. A fully charged battery will have a corrected specific gravity of 1.260; charge if below 1.215.
8. Fill the battery cells to the bottom of the filler neck; add distilled water and recharge if low.

⚠ Ignition of explosive battery gases can result in severe personal injury; do not smoke or allow any ignition source near the battery.

Tools: Battery hydrometer

1. Use a battery hydrometer to check the specific gravity of the electrolyte in each cell.
2. Hold the hydrometer vertical and take the reading.
3. Correct the reading by adding four gravity points (0.004) for every five degrees the electrolyte is above 80 F (27 C), or subtracting for below.
4. A fully charged battery will have a corrected specific gravity of 1.260; charge if below 1.215.