How would you run the return ??

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EL5DEMON340

EL5DEMON340

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I’ve got a brand new spectra fuel tank about ready to go in my 71 demon along with a new 3/8” sending unit. I run a Mallory elec pump and will be using a return style regulator to help ease fuel boil over when parked hot. I will run a 3/8” return back to the tank.

The sender has the small vapor 1/4” fitting so I’m not sure I want to drill that out and try brazing a 3/8” tube on it, risking damaging the sender . Would bringing the tank to a radiator shop and having them braze a tube in next to the sending unit work? Seems like a good option since the tank is new.
What do you think? Thanks again!
 
EL5DEMON340 said:
I’ve got a brand new spectra fuel tank about ready to go in my 71 demon along with a new 3/8” sending unit. I run a Mallory elec pump and will be using a return style regulator to help ease fuel boil over when parked hot. I will run a 3/8” return back to the tank.

The sender has the small vapor 1/4” fitting so I’m not sure I want to drill that out and try brazing a 3/8” tube on it, risking damaging the sender . Would bringing the tank to a radiator shop and having them braze a tube in next to the sending unit work? Seems like a good option since the tank is new.
What do you think? Thanks again!
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The tank is brand new. If you can weld, weld a fitting in the tank and bolt it in.

It’s a bit of a wives tale that you have to fill used fuel tanks with water or inert gas before you weld on them. If the tank has been sitting empty for a couple of weeks there will be nothing left in it to ignite.

If it’s fresh out of the car (or off the bike) then run several tanks of water through it and go.
 
I would silver braze it right into the tank. Start with a small sharp sheet metal awl to form the start of a hole, and enlarge it with a larger one, until the fitting/ tube you are using will barely fit, then braze it in place. Do NOT go small. I went to small because at the time I was just wanting a vapor return system, and later went EFI. I'd put in some sort of fitting you can adapt up or down, or else 3/8 tube. Steel or copper
 
What exactly are we brazing onto the tank though? I'm not sure it makes sense to just stick a fitting or some such thing onto the outside of it. The bulkhead fitting I linked to was literally made for this exact purpose and from my point of view it looks to be much easier to deal with and a better solution.

Understand the OP has a new 3/8" sender but another option could be to get a different one with a built in return nipple. Like this.
 
rmchrgr said:
What exactly are we brazing onto the tank though? I'm not sure it makes sense to just stick a fitting or some such thing onto the outside of it. The bulkhead fitting I linked to was literally made for this exact purpose and from my point of view it looks to be much easier to deal with and a better solution.

Understand the OP has a new 3/8" sender but another option could be to get a different one with a built in return nipple. Like this.
Click to expand...

Are you talking about using that bulkhead fitting in the sending unit or the tank?

In the tank you’d have to place the fitting somewhere that you can get your hand in the tank to use that fitting.

Unless I’m missing something.
 
rmchrgr said:
What exactly are we brazing onto the tank though? I'm not sure it makes sense to just stick a fitting or some such thing onto the outside of it. The bulkhead fitting I linked to was literally made for this exact purpose and from my point of view it looks to be much easier to deal with and a better solution.

Understand the OP has a new 3/8" sender but another option could be to get a different one with a built in return nipple. Like this.
Click to expand...
I have a new sender like that with the vapor/ return but it’s only 1/4”. Return should be the same as the supply side size . Thanks that bulkhead might be the way to go.
 
rmchrgr said:
What exactly are we brazing onto the tank though? I'm not sure it makes sense to just stick a fitting or some such thing onto the outside of it. The bulkhead fitting I linked to was literally made for this exact purpose and from my point of view it looks to be much easier to deal with and a better solution.

Understand the OP has a new 3/8" sender but another option could be to get a different one with a built in return nipple. Like this.
Click to expand...
It was just a suggestion and another option. "What exactly?" Nothing exactly. There are lots of things you can use for fittings, JIC etc steel, various brass, or copper or steel tubing. Frankly, I would find it a lot easier to punch a 3/8 hole and braze in a piece of tube than drill a 9/16 hole. IT IS ONLY a suggestion.
 
"The sender has the small vapor 1/4” fitting so I’m not sure I want to drill that out and try brazing a 3/8” tube on it"

First the electrical portion of the sender is at least 3" away from the heat... So nothing to be concerned with..

Second I agree let a radiator shop do it, they deal with this kinda stuff all the time... But they won't braze it, they will solder it.... Less heat....
 
Soft solder is not what you want on a vibration prone fuel fitting.
 
I did a conversion to EFI using the metal fuel tank recently. I used a fitting similar to the one bulkhead referenced in post #2. I drilled the tank with the sending unit out and was able to get my arm in the sender hole to tighten up the nut on the bulkhead fitting. The customer is driving it now with no leaks.
 
Demonracer said:
I did a conversion to EFI using the metal fuel tank recently. I used a fitting similar to the one bulkhead referenced in post #2. I drilled the tank with the sending unit out and was able to get my arm in the sender hole to tighten up the nut on the bulkhead fitting. The customer is driving it now with no leaks.
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That’s what I was thinking. I know my arm won’t fit in that sending unit hole.

When I added the sump on my tank I also added a return line fitting. Since I had the welder out I just welded a fitting in.

If you can get your hand in there to get to the nut on the bulkhead fitting that is his best option.

Maybe I should have had my kid go out there with his skinny 15 year old arms (he‘s 22 tomorrow) and do it but like I said, I had the welder out so I did it myself.
 
When I did this a few years ago I tried using a 3/8 bulkhead connector (not the same one as listed above) mounted on the sender unit. Problem I had was there just wasn’t enough free room on the sender to mount it. Drilled out the small tube and silver soldered leftover fuel line in its place, been good for 6 years.
 
Yes the sender is tight, I would have to cut and drill out the 1/4” tube and add a 3/8” ..

IMG_5260.jpeg


IMG_5261.jpeg
 
EL5DEMON340 said:
Yes the sender is tight, I would have to cut and drill out the 1/4” tube and add a 3/8” ..
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Yeah, that looks tight especially with the bracket on the back. Tough one.

If you're willing to spend the money, RobbMc makes a 1/2" pickup with a 1/2" return. I had one before I went to EFI, it worked good. I used reducer fittings to step down to 3/8" line. I didn't use a return so it was capped off.
 
Piercing for any reason a brand new tank would be my last option.


And I'm hearing plenty more here.

On the welding on a used tank, I'll stick with the myth, rumor has it the one's that know for certain, aren't here.:rolleyes:
 
J-c-c said:
Piercing for any reason a brand new tank would be my last option.


And I'm hearing plenty more here.

On the welding on a used tank, I'll stick with the myth, rumor has it the one's that know for certain, aren't here.:rolleyes:
Click to expand...

I weld on them fairly regularly. I ain’t dead yet. It’s time for that myth to die a quick death.
 
Newbomb Turk said:
I weld on them fairly regularly. I ain’t dead yet. It’s time for that myth to die a quick death.
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After just retiring from 51 years in a niche high risk unregulated industry and having the best safety record of any of my competitors, I'm not certain if I was just really lucky or good, or some combination.
 
Easy option: Drill the tank, use a bulkhead fitting with a gasket that will seal against the tank.

More over the top answer: Weld a sump on the tank with its own pick up and use the fuel sending unit tube as the return. Note that a cake pan will often work as well as commercial sump kits given how much cutting and welding you'll do.
 
MadScientistMat said:
Easy option: Drill the tank, use a bulkhead fitting with a gasket that will seal against the tank.

More over the top answer: Weld a sump on the tank with its own pick up and use the fuel sending unit tube as the return. Note that a cake pan will often work as well as commercial sump kits given how much cutting and welding you'll do.
Click to expand...
Don't mean too get personal, but has your auto electronics-based employment changed recently, or are you still with the same outfit with new owners?
 
I left DIYAutoTune over a year ago; I now work for a company that makes geotechnical surveying equipment. Any automotive electronics projects you see me working on now are my own pet projects.

And yes - I went the weld-a-cake-pan-to-the-gas-tank route myself.
 
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