Need help with my Onan Generator

Hey Guys
*When I was at the pala motocross national...my generator ran without issues thur and fri. However sat afternoon we fired it up to run the ac and after 20 mins the thing shut itself off. I initially thought no biggie I probably am at a 1/4 tank of fuel which is where it usually will shut the generator off....not the case I checked it and had a half tank. *I went out inspected it, the air filter was clean the oil level appeared correct...when I prime it the fuel pump sounds a bit odd almost as if it's not getting a good prime initially but then sounds like it's pushing fuel (after 1-2 seconds) when I go to start it after that it tried to fire with a lil more rumble than if I don't prime it but still will not fire. I have an appt at the service shop on wed but id really like to avoid that expensive deal if I could.

It's a 2004 onan 4500 (green)
My motorhome is an 04 Winnebago itasca with no fueling station

Thanks for any help gang
CR

I don't know about your specific generator but after owning a wide variety of generators I would check two things. I would look at the condition of your plug(s) which can tell you a lot about the fuel system. Sounds like a fuel issue to me. I would drop the float bowl and make sure it is clean. Most people let gas sit in there generators when they are not in use and the bad gas can cause some problems in the fuel line. I would pull the main fuel line off the carb and check for flow and take a look at your fuel filter during that process.