2006 Raptor 3912 generator will not stay primed with fuel

[Wobitz]

Recently bought a used 2006 Raptor 3912. When first brought home a month ago the generator ran fine. But now it won’t stay running. I’ve replaced the fuel pump and if I put the fuel line from the pump in a can of gas it runs fine but the pump won’t pull fuel from the tank. Tank is full. If I siphon fuel with an air operated siphon and then put the line back on the pump it will run a few minutes but then loses prime. I blew air in the fuel line with the filler cap off and it blew gas out the filler neck. So it doesn’t appear to be blocked I’m baffled. Anyone help me on this

[chuckster57]

Take the fill cap off the tank and try. If it runs then the tank vent is most likely stuck.

[Wobitz]

I tried that. No luck

[chuckster57]

I tried that. No luck

You tried running the gen with the fill cap off?

[Wobitz]

Yes I took it off and tried Same scenario as I described

[chuckster57]

Sounds like its time to start tracing the fuel line. Sorry don’t have much more.

[Wobitz]

I’m afraid I’m probably going to have to drop the tank and check the connections

[chuckster57]

Start at the gen. Drop edge of underbelly and look for any nicks or kinks first.

[Freeheel4life]

Recently bought a used 2006 Raptor 3912. When first brought home a month ago the generator ran fine. But now it won’t stay running. I’ve replaced the fuel pump and if I put the fuel line from the pump in a can of gas it runs fine but the pump won’t pull fuel from the tank. Tank is full. If I siphon fuel with an air operated siphon and then put the line back on the pump it will run a few minutes but then loses prime. I blew air in the fuel line with the filler cap off and it blew gas out the filler neck. So it doesn’t appear to be blocked I’m baffled. Anyone help me on this

Full disclosure, I know nothing about your system and how it is configured. Seems odd that you can siphon fuel from inlet line to pump and blow fuel out the filler. Is there any kind of anti siphon valve at the tank that could be causing an issue?? Or is it just a barbed fitting??

[Wobitz]

Not sure. That is my next step. I’ll have to drop the tank out of the frame to see all that

[travelin texans]

If you've used gasoline with the 10%+ ethanol it may have swollen up the rubber line internally from the tank to the carb. Ethanol is very hard on rubber parts not designed for ethanol use.
Remember back a few years when ethanol was required in metropolitan areas & all the older cars catching fire, the fuel lines weren't designed for ethanol. If the line is ok structurally, it may just be gummed up, ethanol also turns to a crystal/sugar like state when old, looks like an old bottle of honey.
If there's a gas station in your area that sells it, I'd recommend ethanol free fuel for your genny, lawnmower, or any other tools/toys using gasoline. Your newer car or truck was designed for ethanol & burns it fast enough to not cause problems, other than lower fuel mileage, typically 10% ethanol = 10% less mpg.

[Wobitz]

Ok thanks. There was a little fuel in it when I got it but I put about 20 gallons of new fuel in there.

[Wobitz]

UPDATE!! I found the problem. There is a push lock fitting that connects the black fuel line running to the generator to the clear plastic line coming out of the fuel tank. The fitting was no longer holding on the clear fuel line. I replaced the fitting and so far so good!

[HANGAR]

Glad you solved the problem. It seems weird that you weren't leaking any fuel with the push fitting not completely inserted.

[Wobitz]

It started doing the same thing again. So I replaced those fittings altogether and now it will run all day & night if needed

[jdawgcncdaddy]

I have the same issue. I know something is wonky because I can't fill the gas tank without it cutting off every few seconds. I tried the take the gas cap off trick, and it didn't work for me either. I am suspecting clogged or gummed up lines because I can hear the fuel pump trying to prime, but it never gets fuel. genie runs fine if I spray gas in the carb... but my hand gets tired pumping it in after a few seconds :)

[Wobitz]

I’ve read that when the fuel pump gets weak it will work fine when you start it. But will lose pressure when it warms up. I’d try a new pump first and I also put 3 cans of sea foam in my tank also to try to free up anything that might be in there

[jdawgcncdaddy]

I think the sea foam is probably the best case scenario. this one has been sitting for a bit.

[HANGAR]

I had the same issue with my 5500 Onan. It would be difficult to start, but once it did start, it only ran for a few minutes and would then die. Did some trouble-shooting and found the original Onan fuel pump worked, but the flow seemed weak. Replaced it with a universal automotive fuel pump made by Purolator and it now works like a champ. Relocated the pump to an area where it's a lot easier to get to than the factory location. Also replaced the primary fuel filter (near the fuel pump) with a "clear" filter so I can see the gas going through the filter and check the cleanliness of the filter. Saved a ton of money not replacing these items with the OEM Onan parts and the new mounting location now allows me to easily see the gas flowing through the filter.

[jdawgcncdaddy]

I had same issue. I took of the Onan pump and put it directly in a small fuel container, and it would pump "ok" but would not pump from the tank, even if I siphoned it most of the way (side note, gas still tastes terrible). I bought a universal pump, mounted it to the frame beside the generator and it worked perfect. Also, note, I had some pinched spots in the fuel line that I rerouted jst for future proofing. Not sure why someone would mount a fuel line on a sharp pinched edge, when it could go over the top no problem.