From the Cummins Onan website:
How often should I run my gasoline generator to keep it in good condition.
It may seem strange that not using a machine could cause performance problems, but with RV generators that's exactly the case. Regular "exercise" is an important part of keeping your generator healthy. Lack of use can cause moisture build-up and fuel system damage that makes it run poorly. In fact, in as little as 30 days, the fuel in gasoline-powered generators can begin to break down into gums and varnishes that clog the fuel system. Fuel varnishing results in hard starting and surging. (A surging generator never settles at a stable operating speed.)
To prevent such problems, we recommend running gasoline generators at a minimum of 50 percent capacity (for example, 2000 W, or one air conditioner for a 4000 W set) for two hours at least once every four weeks. A long two-hour exercise period is preferable to several short periods.
'14 Winnebago Vista 35F, '14 GMC Terrain
BlueOx Towing Pkg, SMI Stay-n-Play
49 States & 7 Provinces visited in MH | WIT W112365