Cummins/Onan MAJB-1 R Engine Engine

• Run Lamp, Time Meter, or Battery Condition Meter Does Not Operate
  Cause: 1. Open circuit between the control and the remote Start/Stop switch. 2. If the battery condition meter works but the time meter does not, the time meter is defective.
  Fix: 1. Check for continuity and correct if circuit is open. 2. Replace time meter.
• Low Oil Pressure
  Cause: Oil viscosity too light or oil is diluted. Low oil level. Low oil pressure switch defective. Faulty oil bypass valve. Excessive engine wear or defective oil pump.
  Fix: 1. Drain oil and refill with correct viscosity oil. 2. Add oil as required. 3. Replace oil pressure switch (see Engine Block Assembly section). 4. Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section). 5. See Engine Block Assembly Section
• Low Battery
  Cause: 1. Weak or discharged battery. Generator set charger will not recharge a battery that is in a very low state of charge. 2. Load connected to battery while set is turned off. 3. Open in charge circuit due to: a. blown charging fuse or b. open charging diode (CRI).
  Fix: 1. Check and replace weak or discharged battery. 2. Disconnect load from battery when generator set is turned off. 3a. Replace blown charging fuse. 3b. Replace open charging diode.
• High Oil Consumption
  Cause: Oil viscosity too light or oil is diluted. Crankcase breather valve is dirty or defective. Oil leaks. Excessive engine wear.
  Fix: 1. Drain oil and refill with correct viscosity oil. 2. Clean crankcase breather and replace if defective. 3. Locate source of leak and repair as required. 4. See Engine Block Assembly section.
• Engine Starts But Stops When Start Switch is Released
  Cause: 1. Low oil pressure switch not closing due to: a. low oil level, b. open circuit between switch and control, c. defective low oil pressure switch, or d. low oil pressure. 2. Output voltage from generator not being supplied to control due to: a. open circuit in wiring between generator and control, b. defective bridge rectifier, or c. no output voltage from generator.
  Fix: 1a. Check oil level and add oil if low. 1b. Check for continuity and correct if circuit is open. 1c. Replace low oil pressure switch. 2a. Check for continuity and correct if circuit is open. 2b,c. Refer to Generator section for test and service procedures.
• Engine Starts And Runs; Then Stops. Set Restarts Immediately or Set Restarts After Cooling Down
  Cause: 1. Fuel level is below generator set fuel pickup tube or oil level is low. 2. Faulty choke operation due to sticking choke linkage, incorrect choke adjustment, open circuit in wiring between choke heater and generator, or defective choke heater. 3. Vapor lock due to: a. high ambient air temperatures or b. faulty fuel pump. 4. Breaker points sticking. 5. Contaminated fuel.
  Fix: 1. Check fuel and oil levels and refill as necessary. 2. Refer to Fuel System section for testing and service procedures.
• Engine Overheats
  Cause: Restricted water flow due to dirt or debris blocking water inlet passages. Faulty thermostat Incorrect ignition timing. Lean fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, or c. dirt in carburetor. Faulty water pump impeller.
  Fix: 1a. Clean away any debris from water inlet and flush the engine cooling system. 2. Replace thermostat. 3. Adjust breaker point gap. 4a. Adjust carburetor main and idle adjustment screws. 4b. Adjust carburetor float level. 4c. Disassemble carburetor and clean all internal passages. 5. Replace impeller.
• Engine Lacks Power
  Cause: Faulty ignition due to: a. incorrect ignition timing or b. incorrect spark plug gap. Restricted fuel flow due to: a. plugged fuel filter or b. faulty fuel pump. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, or c. dirt in carburetor.
  Fix: 1a. Adjust breaker point timing. 1b. Reset spark plug gap. 2a. Clean fuel filter. 2b. Test fuel pump and repair or replace if faulty. 3a. Adjust carburetor main and idle adjustment screws. 3b. Adjust carburetor float level. 3c. Disassemble carburetor and clean all internal passages.
• Engine Hunts or Surges
  Cause: Sticking or binding governor linkage. Incorrect governor adjustment Faulty governor spring. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, or c. dirt in carburetor. Governor mechanism worn excessively.
  Fix: 1a. Clean and lubricate governor linkage. 2. Adjust governor speed and sensitivity. 3. Replace governor spring. 4a. Adjust carburetor main and idle adjustment screws. 4b. Adjust carburetor float level. 4c. Disassemble carburetor and clean all internal passages. 5. See Engine Block Assembly section.
• Engine Does Not Crank
  Cause: A. open circuit in remote control or b. remote start switch faulty.
  Fix: 1a. Check for continuity and correct if circuit is open. 1b. Replace remote start control switch.
• Engine Cranks But Does Not Start
  Cause: 1. Faulty ignition due to worn or fouled spark plugs, magneto malfunction, worn ignition points, incorrect ignition timing, or faulty plug wires. 2. Faulty fuel system due to sticking choke, faulty fuel pump, or carburetor mixture screws incorrectly adjusted.
  Fix: 1. Refer to Ignition System section for test and service procedures. 2. Refer to Fuel System section for test and service procedures.
• Black Exhaust Smoke
  Cause: Rich fuel mixture due to: a. choke sticking, b. incorrectly adjusted fuel mixture screws, or c. dirt in carburetor.
  Fix: 1a. Clean choke and choke linkage. 1b. Adjust carburetor idle and main adjustment screws. 1c. Disassemble carburetor and clean all internal passages.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan MAJB-1 R.

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.