Generator fuel delivery mystery making me crazy

[Radwinnie]

Hi all,
This is my first post. Hoping someone can help me figure out a fuel delivery problem I'm having with the generator on my 1989 Winnebago Superchief. The generator is an onan emerald III. The problem is that the generator runs great when its pulling fuel from a gas can, but won't start at all when its pulling gas from the rv's main tank. I know.. it sounds like a simple case of clogged fuel line. Well, I've disconnected the fuel line between the fuel pump and the carburetor, and it seems to be pumping plenty of gas. I havent actually measured the fuel pressure, but it looks the same as when its pumping from a gas can. Also, the rv itself runs great and the gas in the tank is fresh, so its not that. When its running off the gas can it fires right up and runs no problem, but when I have it running off the rv tank it won't even fire. I'm stumped. Anyone have any ideas??

[Oz]

Is there a fuel filter between the RV  and the generator?

[DaveVA78Chieftain]

How much gas in the tank?  The tank pickup is designed such that it does not go to bottom of tank so that you do not run the tank dry with the generator.  This way you can hopefully still have enough gas in the tank to get to a gas station.

[Mlw]

As i understand you correctly you have seen the fuel pump pumping gas from the RV tank but then the generator still doesn't start. How large was the amount that came out because if it was just a little bit it could also be that this was still there from the gas can in the diaphragm or the lines.

My guess is that you have the same problem like I do, only I have this problem with my RV engine. You get air in the fueling and then the pump stays running dry.

Maybe some of the answers exodus has given me do apply for you too.
Starting issues/accelerator pump needle

[eXodus]

the emerald has a fuel pump right next to it.

So when that pump actually pumps fuel from primary tank - what you can test out - just remove the hose to the carburetor put it the gas can and let the pump run alone Let it just move fuel from the RV tank to your gas can.

Let it run for a few minutes and see how much gas it delivers. Don't know the exact numbers out of the top of my head but something like a gallon per 5 minutes or so.

The pump might be on it's last leg. Wonder why it doesn't want to fire, at all. When it's not producing any volume the generator will not run.
Either line clogged or pump dead.  Pumps are cheap and fail. Nothing special.