Why generators show "engine misfires at light load": 18 documented causes and brand-specific fixes, compiled across 9 manufacturers.
Carburetor idle jet clogged. Spark plug gap too narrow. Intake air leak. Faulty ignition.
2 brands- Cummins/Onan: Clean. Adjust to correct gap. Tighten or replace gaskets. Clean, adjust, or replace breaker points, spark plug, condenser, etc. Poor compression. Tighten cylinder head and spark plug. If still not corrected, grind valves. Replace piston rings, if necessary.
- Doosan: Clean. Adjust to correct gap. Tighten or replace gaskets. Clean, adjust, or replace breaker points, spark plug, condenser, etc. Poor compression. Tighten cylinder head and spark plug. If still not corrected, grind valves. Replace piston rings, if necessary.
Carburetor idle jet clogged or improperly adjusted. Spark plug gaps too narrow. Intake air leak, Faulty ignition.
2 brands- Cummins/Onan: Clean or adjust. Adjust to correct gap - .025"{.018" for gas operation). Tighten manifold and carburetor mounting screws. Replace gasket if necessary. Clean, adjust, or replace breaker points, spark plugs, condenser, etc.
- Onan Electric: Clean or adjust. Adjust to correct gap - .025"{.018" for gas operation). Tighten manifold and carburetor mounting screws. Replace gasket if necessary. Clean, adjust, or replace breaker points, spark plugs, condenser, etc.
Carburetor idle jet clogged or improperly adjusted. Spark plug gaps too narrow. intake air leak. Faulty ignition.
2 brands- Cummins/Onan: Clean or adjust. Adjust ‘to correct gap -025” (.018” for gas operation). Tighten manifold and carburetor mounting screws, Replace gaskets if necessary. Clean, adjust, or replace breaker points, spark plugs, condenser, etc.; Clean or adjust. Adjust ‘to correct gap -025” (.018” for gas operation). Tighten manifold and carburetor mounting screws, Replace gaskets if necessary. Clean, adjust, or replace breaker points, spark plugs, condenser, etc. or retime ignition.
- Prestolite: Clean or adjust. Adjust ‘to correct gap -025” (.018” for gas operation). Tighten manifold and carburetor mounting screws, Replace gaskets if necessary. Clean, adjust, or replace breaker points, spark plugs, condenser, etc. or retime ignition.
Spark plug gap too narrow
2 brands- Cummins/Onan: Adjust to correct gap
- generatorpartspro: Adjust to correct gap Tighten or replace gaskets Clean, adjust, or replace breaker points, plug, condenser, etc., or retime ignition
Carburetor idle jet clogged or improperly adjusted. Spark plug gaps too narrow. Inadequate air leak.
2 brands- Garretson: Clean or adjust, Adjust to correct gap - .025" (.018" for gas operation). Tighten manifold and carburetor mounting screws. Replace gaskets if necessary.
- NEC: Clean or adjust, Adjust to correct gap - .025" (.018" for gas operation). Tighten manifold and carburetor mounting screws. Replace gaskets if necessary.
Carburetor adjustment set wrong or clogged. Spark plug gap too narrow. Intake air leak. Faulty ignition.
1 brand- Cummins/Onan: Adjust, clean if needed. Adjust to correct gap. Tighten or replace gaskets. Clean, adjust or replace breaker points, plug, condenser, etc. Clean and adjust.
Carburetor idle adjustment set wrong or clogged.
1 brand- Cummins/Onan: Adjust, clean if needed.
Carburetor idle adjustment set wrong or clogged. Spark plug gaps too narrow. Intake air leak. Faulty ignition. Uneven compression.
1 brand- Cummins/Onan: Adjust to correct gap. Tighten or replace gaskets. Clean, adjust, or replace breaker points, plugs, condenser, coils, etc., or retime ignition. Tighten cylinder head and spark plugs. If still not corrected, grind valves. Replace piston rings, if necessary. Worn intake valve stems. Replace valves.
Spark plug gap too narrow. Intake air leak. Faulty ignition. Low compression.
1 brand- Cummins/Onan: Adjust to correct gap. Tighten or replace mani- fold and carburetor gaskets Clean, adjust or replace spark plugs. Tighten cylinder head ar spark plugs. Grind valve; Adjust to correct gap. Tighten or replace manifold and carburetor gaskets. Clean, adjust or replace spark plugs. Tighten cylinder head and spark plug.
[Faulty injection. Poor compression.
1 brand- Cummins/Onan: Inspect fuel system for faulty injection issues. Check and address poor compression if present.
Carburetor idle jet clogged or improperly adjusted. Spark plug gaps too narrow.
1 brand- Cummins/Onan: Clean or adjust. Adjust to correct gap.
Intake air leak, Faulty ignition, Poor compression
1 brand- Cummins/Onan: Tighten or replace gaskets, Service ignition, Tighten cylinder heads and spark plugs. Repair engine.
Improper choke operation
1 brand- Cummins/Onan: Clean cylinders, See Sect 3.2.1.
Carburetor idle adjustment set wrong or clogged. Spark plug gaps too narrow. Adjust to correct gap. Refer ta TABLE OF CLEARANCES. Intake air leak. Tighten or replace gaskets. Faulty ignition. Clean, adjust, or replace breaker points, plugs, condenser, coil, etc., or retime ignition, Uneven compression. Tighten cylinder head and spark plugs. If still not corrected, grind valves. Replace piston rings, if necessary.
1 brandCarburetor, idle jet clogged or improperly adjusted, Spark plug gaps too narrow, Intake air leak.
1 brand- Cummins/Onan: Clean. Adjust to correct gap. Tighten manifold and carburetor mounting screws. Replace gaskets if necessary.