I have a Onan QC4000 generator that is 5 years old about 500 hours. This spring the generator would start and run for around 3 to 5 minutes and shut down, after a shutdown it would not stay running more than a few seconds until it cooled down for several hours.
I replaced the Carb, air filter, fuel filter, Gas pump, spark plug, ( aftermarket fuel pump )
and the generator still had same issue. Read many forums, tried many tests. Tried diferent aftermarket fuel pump, still shut doen after a few minutes. Decided to try a OEM fuel pump , read many reviews about low pressure pump, still same issue, probably run shorter time with this pump.
Decided to call Flight Systems they provide free technical assistance, the technician was very good, suggested to measure the slip rings resistance and magnetor resistance, all were good.
Next step for me was try replacing the Control board with a Flight Systems aftermarket board which does not monitor every small thing and shutdown. If this board did not work they would take it back for 25% restocking fee, the board was $400 compared to Onan board at over $600.
Bingo, this solved my shutdown problem, generator has run over 2.5 hours with AC running and no shutdown.
