1972 J4000 Camper Special

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redrambler1966
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Joined: Sat Sep 22, 2018 10:01 pm
Location: OryGone

1972 J4000 Camper Special

Post by redrambler1966 »

Just bought this Bad Boy a few weeks ago and cannot get fuel to the fuel pump. Somewhere in her past, someone swapped a Chevy 454 into her along with a bed mounted 60 gallon auxiliary gas tank. She already had the stock tank and a factory "auxiliary" tank............total fuel storage is now at 90+ gallons. Guess at 6 MPG, she needs that much fuel capacity. Looks like the factory "auxiliary" tank fits directly above the stock tank. No selection valves were installed for these two smaller tanks. I need a factory installation manual for these two tanks to determine what my problem might be. Looks like the factory supply line from the stock tank was 3/8" diameter, but at some point was spliced down to 5/16"................just curious if this size restriction my not allow the fuel pump enough suction to pump fuel from the stock tank to the fuel pump.

With the gas cap removed and a disconnected supply line that goes into the pump, no fuel is present at the fuel pump.............but I can blow air into the tank and hear the bubbling of same.

Again an idea of the "plumbing" required by the stock tank and the factory "auxiliary" tank would be helpful.
1972 J4800 Camper Special (w/454 BBC)


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tgreese
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Re: 1972 J4000 Camper Special

Post by tgreese »

If there's a leak in the line from the tank to the pump, the pump will just suck air. Like a soda straw with a hole in it. Likely your lungs have enough capacity that you can make bubbles in the tank, even with the hole there. if you can't inspect the line all the way from the pump to the tank (you can't see the top of the factory tank), you might be able to test it by pulling fuel into the line with a MityVac, and seeing if the gas drains back itself. Or you could blow gently into the line and see if you can push air through without bubbling in the tank.

The '72 TSM has a very good drawing of the factory tank and plumbing. No drawing of any auxiliary though. I don't recall any factory equipment like that, and neither the TSM or my '74 parts book has any mention of aux tanks. Where is it located? You sure it's not aftermarket or adapted from another application?

The '72 TSM is cheap on CD-ROM from RockAuto.

Image

The little hose connected to the fuel tank sender is likely rotted.
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1971J4000
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Re: 1972 J4000 Camper Special

Post by 1971J4000 »

I have the same setup in my 71 J4600.

The auxiliary tank simply gravity feeds to the tank below it. Has no valves and would not be a source of the issue inre to fuel pump issues.

I do not have a printed diagram... but if you need pictures of my setup I can get some for you.

Now on the side of your truck you should have an upper & a lower filler cap.

Never fill your tank from the bottom one. I siliconed my closed so no one accidentally uses the lower filler cap.

Always fill from the top filler cap and gravity will keep the bottom take full.
1971 J4600 with Dauntless 350

Herk
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Re: 1972 J4000 Camper Special

Post by Herk »

I have dual tanks on my 71, but my aux tank is behind the seat (looks like a Chevy truck tank, probably a dealer or first owner mod). There is no way that fuel can gravity between tanks, but the fuel return line only goes to the rear (factory) tank. Must use the rear tank first otherwise return fuel will overfill the rear tank and spill overboard.
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