Generator engines are like any engine, they need to be run to preform the best.
ONAN for the HGJAA, HGJAB, HBJAC typical 5.5 or 7.0 gensets recommends exercising the generator at least 1 hour per month if used infrequently. This drives off moisture, re-lubricates the engine, replaces stale fuel in the fuel lines and carburetor and removes oxides from the electrical contacts and generator slip rings. The results are a better starting, more reliable operation and longer engine life.
ONAN recommends checking the engine oil every 8 hours, clean the spark arrestor every 50 hours, change the engine oil, oil filter, air filter every 150 hours or once a year and replace the spark plugs and fuel filter every 500 hours.
ONAN RV Generator Handbook.
Download the following manuals for your HGJAB from