How to Troubleshoot an Onan Emerald Genset 1 Generator

How to Troubleshoot an Onan Emerald Genset 1 Generator

Explore America's Campgrounds

Onan opened for business in 1925. Cummins acquired the company in the mid 80's, becoming Cummins Onan. The Onan Emerald Genset 1 generator is one in a series of generators with two cylinders and opposing pistons, mostly found in the RV industry. Cummins Onan is a world leader in the small genset field, but wear and tear will inevitably occur -- as with any engine. A little preventive maintenance and troubleshooting will go a long way toward keeping your generator efficient.

Items you will need

  • Spark plug socket wrench

  • Wire brush

  • Spark plug

  • Distilled water

  • Goggles

  • Rubber gloves

Step 1

Check the battery electrolyte levels if the generator cranks too slowly, or fails to crank at all. Add distilled water as needed to reach the split-level marker in the battery. Make certain that the battery cable connections are clean and secure. Wear goggles and rubber gloves when troubleshooting the battery. Check the fuse on the control panel. Replace the fuse if it is blown.

Step 2

Verify that the fuel supply shut-off valve is fully open if the engine cranks but will not start. Open the fuel tank and check the fuel level. Add fuel if the level is below the genset pick-up level.

Step 3

Replace or clean the air filter. Remove the through-bolt on the side of the air cleaner housing. Remove the air cleaner housing, taking care not to damage the air pre-heater hose that is attached to it. Take out the air filter element and blow it clean with compressed air. Replace the filter by properly aligning it with the housing.

Step 4

Clean or replace the spark plug if the engine runs but tend to surge. Unscrew the spark plug with a socket wrench. Brush any black carbon deposits from the plug. Replace the plug if it is damaged in any way. Use a spark plug feeler tool to check the electrode gap. The gap should be 0.64mm. Check the security of the spark plug leads at the plug. Replace the leads if they are worn.

Step 5

Remove the oil level indicator to check the oil level. Wipe the excess oil with a clean cloth. Screw the indicator back into the normal operating position. Unscrew the indicator and check the oil level on the end of the indicator stem. Add oil until it reaches the "Full" mark on the indicator. Do not overfill. Screw the oil indicator back into place.


  • Overfilling the battery cells can diminish the life of the battery.
  • Do not fill the generator fuel tank while the engine is running.
  • Provide an adequate exhaust system to the generator to properly expel discharged gases. Exhaust fumes can be deadly.
Gone Outdoors