1978 Suburban fuel fill issue

[Advanced Design]

Guys, appreciate your ideas on this one. A buddy just completed an LS swap on this 78 Burb. Filling the fuel tank is very slow and difficult. Condition existed before the swap. Still exists with the vent disconnected at the tank. Gas just backs up in the fill pipe.

I've searched for ideas here and I did find several threads about the issue on trucks with no good solutions.

We figure it is the small diameter of the fill pipe coupled with the very slight down angle that causes the fuel to back up. Tanks inc has a larger diameter tank neck that we will try.

Unless there is something I am missing? Appreciate your ideas.

[Advanced Design]

Fill pipe...

[Advanced Design]

Fill

[mongocanfly]

I think your on the right track...your displacing air with fuel...I would think the fill vent is the issue...as long as the vent is behind the pump nozzle it should work...I assume yall made sure the vent tube isn't clogged or kinked...but I guess you eliminated that by removing the vent at the tank...maybe its the tube inside the tank...

[68Timber]

Originally Posted by mongocanfly

I think your on the right track...your displacing air with fuel...I would think the fill vent is the issue...as long as the vent is behind the pump nozzle it should work...I assume yall made sure the vent tube isn't clogged or kinked...but I guess you eliminated that by removing the vent at the tank...maybe its the tube inside the tank...

I'm still wondering about the vent because they fill fine with stock hardware when in good order. You removed the vent lines, did you blow out the hard line on the tank where the vent lines connect? Run a pipe cleaner through it if you can.

[Advanced Design]

Originally Posted by 68Timber

I'm still wondering about the vent because they fill fine with stock hardware when in good order. You removed the vent lines, did you blow out the hard line on the tank where the vent lines connect? Run a pipe cleaner through it if you can.

Good idea John. The vent through the sending unit is clear and tank still didn't want to fill with the vent hose disconnected at the new sender. Here is is removed from the tank.

[Advanced Design]

Thanks Mongo. Yes, fill issue still exists with the vent tube open at the tank.

[mongocanfly]

I wonder if the fill tube has a restriction...may need to pull the tank and have a looksee...what's that hose clamp in the middle of the fill tube in the last pic?....something looks odd about the hose right there...looks like a hose stuffed inside a hose...

[Advanced Design]

Originally Posted by mongocanfly

I wonder if the fill tube has a restriction...may need to pull the tank and have a looksee...what's that hose clamp in the middle of the fill tube in the last pic?....something looks odd about the hose right there...looks like a hose stuffed inside a hose...

Will check and verify. Appreciate the input!

[Advanced Design]

Under hood shot just because we all like pic's. Swap was completed using the Holley mounts.

[kwmech]

May be an anti-siphon device in the metal part of the filler tube?. Loosen a couple of hose clamps and undo a couple of screws and remove the filler neck completely then have a look see. The 'burbs did not change a whole lot in the 18 years they were built. I'm on my 3rd square body without a problem filling the tank

[Advanced Design]

Originally Posted by mongocanfly

I wonder if the fill tube has a restriction...may need to pull the tank and have a looksee...what's that hose clamp in the middle of the fill tube in the last pic?....something looks odd about the hose right there...looks like a hose stuffed inside a hose...

There were no restrictions in the hose. The small diameter seems to fill and back up, similar to a funnel with a small neck.

Looking at making use of Tanks 2" elbow at the tank for a larger diameter fill hose.

[mongocanfly]

sounds like a good plan..

[Advanced Design]

Originally Posted by mongocanfly

sounds like a good plan..

Hope so, like Kwmech mentioned above he has had three of this body style with no problem on the fuel fill. This one just isn't happy.

And it could always be something simple we overlooked...keeps us all humble when we do that. Ha...

[Advanced Design]

Thanks KW, will do.

[cheepin]

How are you filling the tank? At a gas station pump or with a container? More then one station if at a station? Maybe the pumps at the station are too fast. I have had that problem before. My 84 crew cab diesel has to be only on the first stop with the new diesel pumps. Our gasser Sub. most pumps are fine but every once and a while one will be too fast.

[Advanced Design]

Cheepin, good thought. A hand held gas can would overfill the fill pipe causing a back up. Happened with any pump too.

My buddy replaced the smaller neck and fill with the 2" diameter one. That eliminated the problem with filling the tank.

Appreciate all the input guys.

[68Timber]

Interesting. The stock neck looked normal when removed?

[Advanced Design]

Originally Posted by 68Timber

Interesting. The stock neck looked normal when removed?

Yes, there were no restrictions noted on the fill side.

[phillipm]

I don' know about you guys, but on my Blazer if I hold the fuel handle all the way tilted up so the nozzle is pointing as far down as possible, mine will fill correctly. My opinion is it's just the fill port is at the wrong angle. You'll notice all newer vehicles have the fill tube in the car at like an 75* angle which matches the pump fill nozzle.