Onan generator not getting gas

The gas cap should be unvented so I don't think that's the problem. The carbon canister is the vent for the tank. Given what you've found it's likely that or the line to it are the problem.

Thanks for posting your find. Never would of thought of that! I take it you recently changed the cap? It is uncanny how many problems can be tracked back to a change that was made that shows no apparent relation to the actual problem component. Sometimes when I am stuck on a problem I just sit down and think "what I have I changed lately?" and often that leads me to a solution.

Thank you everyone for the advice and help. After replacing several parts, lots of hours and frustration, I believe we have found the problem...the wrong gas cap!!!! Take the cap off and the generator starts right up and runs great. Go figure! Thanks again. I appreciate this forum.

Yeah kind of like what I said, but the same

Captain JL wrote:
Yes, we replaced the fuel filter and the hose lines to the gas tank. We got the generator started once and let it run for a few minutes, then shut it off thinking it would restart. No such luck. It will start using an auxillary tank, so it must be the fuel line feed. How does the fuel line feed into the gas tank?

Most fuel line feeds I have seen have a stinger that mounts into the fuel tank and protrudes into the tank. I noticed that you did replace the fuel filter and lines and did have the generator running for a few minutes then nothing unless you operate from a remote tank. I would venture to say that either you have something blocking the fuel intake at the stinger, In which case you could simply back blow the line with compressed air, or you have a airlock in your fuel feed in which case you should pressurize your fuel tank with compressed air. Either way you should be very gentle and only short burst of air are to be used.
Good Luck

@ pitch...I am not trying to steal your thread I am simply giveing advice which I thought was the goal.

Yes, we replaced the fuel filter and the hose lines to the gas tank. We got the generator started once and let it run for a few minutes, then shut it off thinking it would restart. No such luck. It will start using an auxillary tank, so it must be the fuel line feed. How does the fuel line feed into the gas tank?

Did you also change the fuel filter when you changed the fuel pump?

NOT OSHA APPROVED!!!!! Loosen your gas cap, open the line between your filter and tank. Give a shot of compressed air backwards into the tank(small shot 10 or 15 # max for a second.) Gas may erupt from the tank beware.
My thinking is that if it is just gravity feed from the tank to the filter you may have a blockage.
Having this problem with 3/4 tank sucks. Either drive the tank down or feed the ONAN from a remote source if you need the generator.

Another thought; Ethanol gas may not be compatible with your lines and they have broken down internally.

Our Onan fuel lines were cracked in our 2004 DP. We took it to Cummins Coach Care and they fixed it quickly and for a fair price.

I would trace the hose back to gas tank. Take off hose and add a short piece of hose and a suction device to narrow down problem. If gas come out of the tank by the tank probably just hose. That fitting could be clogged in the tank. If not just replace the hose.