72 Demon fuel fill vent tube ideas?

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northeastmopar

northeastmopar

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I was just going to drill a 5/16" hole up high on my fuel neck and weld in a short 1" long piece of 5/16 fuel line so I can slide a rubber hose over it to make the bend to go back to hard pipe and down through the filler neck floor grommet out to the ground. Problem is that the fuel neck on my 72 demon gets installed from the outside in and just fits through the hole in the quarter. So anything I try and weld to the neck will not allow me to then install the neck? Plus I want to be able to remove it as well if I need to pull it back out. Anybody got a good way to accomplish this? What if I just bought and used a vented gas cap? Will that do the same thing?? Or do I need to have this vent. Nothing running up front either.
 
72 should have had a charcoal canister. I think. It shoulda had factory venting somewhere. Slide under the tank and look up to where the supply hose starts at the sender.There should be an additional steel tube coming from above the tank somewhere close by.It might be off to the passenger side, I can't recall.The early models had a 4-corner venting and later had just a single.
But to answer your question, yes you can buy a vented gas cap.
Be advised tho that the vent has to work in both directions. It needs to allow air into the tank to replace the fuel that is being drawn out during useage,AND it has to vent pressure build-up on hot days.
 
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AJ/FormS said:
72 should have had a charcoal canister. I think. It shoulda had factory venting somewhere. Slide under the tank and look up to where the supply hose starts at the sender.There should be an additional steel tube coming from above the tank somewhere close by.It might be off to the passenger side, I can't recall.The early models had a 4-corner venting and later had just a single.
But to answer your question, yes you can buy a vented gas cap.
Be advised tho that the vent has to work in both directions. It needs to allow air into the tank to replace the fuel that is being drawn out during useage,AND it has to vent pressure build-up on hot days.
Click to expand...

Wouldn't the vent I install on the fill tube achieve that? I just need to figure out how to do it and still be able to slide the fill tube into the quarter panel hole and down into the tank. The 72 fill tube gets installed from the outside of the quarter panel and the hole is only large enough for the tube? Design needs to be able to be installed and removed from inside the trunk before trying to pull the fill out if needed? A lot of fill tubes are installed and the lip goes up against the inside to the quarter panel. The 72 demon the lip goes against the outside of the quarter?
 
If you are going to weld anyway I suggest you weld a fitting into the neck flush and then screw the fitting for your tube into that.
Just put a section of pipe in the fitting to protect the threads and when done grind or sand any rough edges off flush.
 
Yep, easy way would be to weld a 1/4" NPT bung on the inside of the tube, then once its installed in the car screw in a barbed fitting for a rubber vent hose. You could get fancy and make it all out of metal tubing too.
 
Just a thought but is it possible to actually install the tube from the inside like the older cars? I realize you'd have to "do something" about the screws
 
AJ/FormS said:
72 should have had a charcoal canister.
.
Click to expand...

According to the shop manual. 72 and 73 manual, does not use the vapor separator This was built into the tank, with a single vent line and no separate separator. If THAT was the case you could run that single line "up high into the truck, then back down above the tank IE high in the wheel well, etc.

But if his car still uses the vapor can separate, you would have to retain the vapor can for the tank

Top photo is 71, requiring vapor can. Bottom photo is 72-73 showing one vent line, separator built into tank

71tank.jpg


72tank.jpg
 
Part of "this stuff" is why I settled on a 67. (Pre smog). At the time I was looking, Spokamentro (WA STATE) was causing smog problems in IDAHO. The EPA of course has a monitoring station, and there were people "making noise" about passing and reuiring smog inspections here in N Idaho. (There are two counties, I think, in S Idaho that require inspections)

At the time I did not know that AZ requires inspections on 67 cars, which should by default be outlawed. THERE WAS NO smog specifications for 67 emissions other than CA state, and federal cars were exempt
 
67Dart273 said:
Part of "this stuff" is why I settled on a 67. (Pre smog). At the time I was looking, Spokamentro (WA STATE) was causing smog problems in IDAHO. The EPA of course has a monitoring station, and there were people "making noise" about passing and reuiring smog inspections here in N Idaho. (There are two counties, I think, in S Idaho that require inspections)

At the time I did not know that AZ requires inspections on 67 cars, which should by default be outlawed. THERE WAS NO smog specifications for 67 emissions other than CA state, and federal cars were exempt
Click to expand...

I have already installed a new gas tank. My new sending unit is a 3/8" with no vent, so I was planning on the fill tube vent line, but ran into the snag of how to prep it to install the line from inside the trunk. And if I try to install the fill tube from the inside, the stock cap will fit too deep into the quarter panel. So the 1/4" bung welded into the inside appears to be the best choice to accomplish this?
 
If the tank is for the correct year, the vent is in the tank, NOT the sender

You tank should match the diagram I posted above.

Otherwise, I'd say yeh, weld a flush fitting in. That should be easy, say, if you can silver braze. "Mike" the fender hole so you know what you have to work with. You might be able to notch the fender hole a bit if the gasket will cover it.
 
67Dart273 said:
If the tank is for the correct year, the vent is in the tank, NOT the sender

You tank should match the diagram I posted above.

Otherwise, I'd say yeh, weld a flush fitting in. That should be easy, say, if you can silver braze. "Mike" the fender hole so you know what you have to work with. You might be able to notch the fender hole a bit if the gasket will cover it.
Click to expand...

Yes, The new tank did have a vent tube high up in the front which I plugged shut as I did not want to run a line and do not have a charcoal filter. I was intending on doing the older style vent in the fill tube, but as I said, the fill tube goes into the quarter panel from the outside with no room for anything but the tube to pass through. So I am trying to figure out how I can install the threads without having them protrude so I can screw in a fitting after the tube is installed. How do these bungs work in a curved wall of a tube/exhaust ect without sticking out?
 
Get a long pair of needle nose to hold the nut (bung) on the inside of the filler tube, then weld it from the outside. If there are any gaps due to the tube being rounded, they'll be filled with the weld to seal them up, then just metal finish the outside to make everything smooth if needed.

I like this idea and might need to copy it. I ended up modifying the inner part of a vented gas cap to allow it to vent both ways, it's probably not the best way to do it, but it fixed the issue I was having with the tank becoming pressurized from my EFI return line.
 
I gotta tell you guys. I would not in the least be afraid to try this. But if the tank has the SINGLE vent into the tank, this means the vapor separator is integral. I would simply fab a tube/ hose off that tank fitting, run it up into the trunk beside the filler just like the early vent, "U" bend up by the top and (to keep it high and prevent siphon) run it down into "near the top" of the wheel well from the trunk.

You want to end it up high to prevent siphon. The reason the fill tube type vent can be "so low" is that the fill tube itself forms a vacuum break. Only way it can siphon is if the tank is so full that the fuel is clear up in the filler.
 
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