Repair Tips for Onan Generators

The Onan Generators are produced by Cummins Power Generation, a division of Cummins Diesel. Generators are available in gasoline, diesel or LP models. Power generation capacity ranges from 1,400 to 3,800 watts. The larger capacity generators are capable of powering a 15,000 BTU air conditioner along with some other small electrical appliances. Consult the owner's manual of the appliances for the estimated power draw to calculate what appliances can be powered by each generator model.

Cranking Issues

If the Onan generator cranks but fails to start, probable causes include low oil level, carbon deposits on the spark plugs, the fuel supply cutoff valve is not open or the fuel is below the pickup level in the tank. Solutions to these scenarios include adding oil, replacing the spark plugs, ensuring the cutoff valve is open or adding fuel. For a generator that slowly cranks, examine the battery and its connections, the oil viscosity and the load connected to the generator. If the generator fails to crank completely, it may potentially be a low battery or a bad connection or possibly a blown fuse.

Intermittent Starts and Stops

The Onan generator starts, runs for a short time and then stops or stops when the start switch is released. Check for low fluid levels, including both fuel and oil, or check for overheating due to a blocked airflow. No alternating current output is another potential cause of this symptom. In this instance, contact a professional repair technician rather than troubleshooting on your own.


When the generator runs but surges frequently, it may be an indication of loose or faulty spark plugs. Also, the ignition coil or wiring may be defective or the governor is out of adjustment. Look for carburetor icing or varnishing, in which case a fuel system cleaner may be useful.


Occasionally the Onan generator may exhaust black smoke, which is potentially caused by a dirty air filter or a maladjusted or stuck choke. Replace the air filter; if this does not alleviate the problem, you will want to contact a certified repair technician to properly adjust the choke.