I found the quickest, easiest way to troubleshoot my Onan 4k on my old '83 Tioga, when I got it, was to disconnect the fuel line at the fuel pump on the genny. Very easy to get to. Then connect a fuel line to the fuel pump and drop the other end into a small gas can. If it runs like that, the problem is between the fuel pump and the tank. (BTW, easy way to run a high concentration of seafoam and gas thru the genny this way).
1. enough fuel in the tank? Genny pickup is higher than the engine pickup so the genny can't strand you by running the tank dry
2. Cracked or clogged lines between tank and genny? Blow backwards from genny to tank and listen for airflow into the tank or along the fuel lines for leaks.
If it doesn't run, is the fuel pump running? My old Onan fuel pump could both be heard and felt when running. When it quit, easy to detect. Also, easy to open up, unstick and clean up, return to service again, in my case.
If fuel pump runs but genny doesn't, then you need to refer to more detailed troubleshooting docs.
Good luck!
'07 Ram 2500 CTD 4x4 Quad Cab
'10 Keystone Laredo 245 5er