Fuel leaking from within the generator

That is a very dangerous situation...take it very serious!

The fuel like going to the generator I believe *IS* gravity fed. I believe this because when you change the fuel filter you have to pop off that fuel line and it immediately starts leaking gas and you need to plug it while you change the fuel filter.

It stops leaking at 1/4 tank, because that's as low as your generator can draw gas from the main tank (BY DESIGN).

If you are lucky, the fuel line is leaking at or before it gets to the fuel filter. That might be an easy fix.

Do you see clamps of some sort where the fuel line connects to the fuel filter. If staring at the generator, the fuel line can be found outside the generator coming in from the left side.

Do you see gas in the bottom tray of the generator?? If so, perhaps it is leaking from inside the cover somewhere.

Since your generator wasn't running, it is a gravity fed issue and should be leaking somewhere before the fuel pump.

-Chris

Whataday,

WOW!!! THAT is a LOT of fuel to leak out.

I'm not sure if your Onan 400 shares a similar design to our Onan Marquis Gold 7kWatt (also gas). I'm going back a number of years here, so hopefully my memory isn't too far off. I can tell you that originally my generator had two fuel filters: one right on the generator and another before the generator fuel pump. It was kind of strange, but that's the way they did it.

Well, getting the fuel lines on the filter on the generator tight enough so they wouldn't leak was a bit of a trick. It was behind the air cleaner housing. If you completely removed the air cleaner housing assembly, you could generally get things tight enough. But if you tried to take a shortcut and not remove the air cleaner assembly, you couldn't get the connections tight enough and it would eventually vibrate loose and leak. I noticed mine leaking one time. This was a couple of weeks after I did the fuel filter change. It didn't leak immediately after I changed the filter.

When I went to the local Onan parts distributor, he sold me a "new" filter kit. It only had the one filter that went down by the fuel pump and a little doodad (technical term) which permanently replaced the filter mounted on the generator. It was a short length of tube which had six sides (like a nut) so that it could easily be tightened with the air cleaner assembly in place. Apparently, the leaking was a very common problem, so they removed one of the filters from the system and replace it with this new part. Since this new "doodad" didn't have to be serviced, it minimized that leaking issue once it was installed properly.

Here's a link which talks about the Onan gas fuel filters. Again, this was for the Onan Marquis Gold generators.

Again, I have no idea if your 4000 series is similar, but if it is, perhaps that's the problem. Check to see if there is a filter mounted on the generator and if it's leaking fuel, or looks like the source of the leak. Perhaps your generator never got the update kit.

Good Luck,

~Rick

Fuel leaking from a carburetor almost always means a colored needle valve or sunk float. Yes, the carburetor needs to be removed.

It seems virtually impossible for fuel to drain from the main tank via the generator fuel line. Generator is not (well shouldn't be and not in my experience) gravity fed.
Shouldn't be possible to lose significant fuel out of the tank unless there's a hole in the tank itself. All the fuel pickups come out the top of the tank. Unelss a full line literally was cut and was able to pull a siphon until it emptied the tank.