Best way to vent fuel tank?

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Evan Dutch

Evan Dutch

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Hey guys,

I’m getting around to finishing the fuel system of my 1971 Plymouth Scamp. My new fuel filler neck is not vented and I’m running a new tank like the one pictured. This car is EFI, the pump is mounted outside of the tank.

What would be the best way to vent this setup? Could I utilize one of the 4 ports that are circled in the pic? Or is there a better way?

Thanks,

Evan

IMG_8752.jpeg
 
If the ports are above the fuel level yes.

BUT...

be sure you run HARD line from there up into the trunk make a u turn and go back out of the trunk and terminate in the frame rail like the OEM did.
 
What I did was used a small drill and put a hole in the top of the fill tube. Then I put a punch through and made it bigger until a 1/8 pipe tap could be threaded in. I installed a hose barb. Then ran a braided AN hose up to the top of the quarter panel and strapped it down the tube through the fill tube rubber trunk seal through the floor. Same as all the 67 through 70 a bodies were done with a metal tube.

You could also look for a 67 through 70 fill tube and cap for a Dart

Here are pictures of what I did . The car was wrecked and no fuel spill or fire. The reason I didn't use a 70 duster style is because I already had two 71 caps painted.

Being your car is a scamp and if you want to replace the tube you will need to use a Dart tube. Duster will not fit

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Here is a picture of a 67-70 dart with factory vent tube

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Dana67Dart said:
If the ports are above the fuel level yes.

BUT...

be sure you run HARD line from there up into the trunk make a u turn and go back out of the trunk and terminate in the frame rail like the OEM did.
Click to expand...
What is the purpose of making the line into a U shape? Is it necessary?
 
Oldmanmopar said:
What I did was used a small drill and put a hole in the top of the fill tube. Then I put a punch through and made it bigger until a 1/8 pipe tap could be threaded in. I installed a hose barb. Then ran a braided AN hose up to the top of the quarter panel and strapped it down the tube through the fill tube rubber trunk seal through the floor. Same as all the 67 through 70 a bodies were done with a metal tube.

You could also look for a 67 through 70 fill tube and cap for a Dart

Here are pictures of what I did . The car was wrecked and no fuel spill or fire. The reason I didn't use a 70 duster style is because I already had two 71 caps painted.

Being your car is a scamp and if you want to replace the tube you will need to use a Dart tube. Duster will not fit

View attachment 1716175198

View attachment 1716175199

Here is a picture of a 67-70 dart with factory vent tube

View attachment 1716175203
Click to expand...
I have a new fuel neck in the box so I’ll use the one for a 1971 scamp. Did you make your hose into a U shape like the factory pipe? Also, whenever the hose exits the floor where Did you ultimately run it to?

Did you have any issues with threading your fitting into the filler neck? The tubing wall of the filler neck should be thick enough to accept a tap right?
 
Evan Dutch said:
What is the purpose of making the line into a U shape? Is it necessary?
Click to expand...
It breaks a siphon. ON a hot day, with the tank really full, the fuel can back clear up into the fill tube, especially parked on a hill AKA Seattle/ San Fran, and siphon out the vent onto the ground. With the "U" as soon as the fuel gets low enough it will pull air and stop. The fuel cannot flow out again, until it backs clear up to the top of the U level wise. If you are driving, you may use enough that it won't siphon again, or if cooling towards the end of day, the fuel may subside on it's own.

If you can silver braze or conventional braze, or even gas weld, you could braze a fitting into the neck On a car where the neck goes in from the outside, you need to keep the fitting fairly flush so it will clear the fender hole
 
I'm curious - the factory tanks with 4 nipples had a "tank inside the tank" maybe a gallon or so in capacity. - part of the emissions system. Does your tank have that? I can't figure out how the 4 nipples work without that and those tanks had a rubber plug in the top of the tank to drain that little tank. I don't see that plug on on yours...
 
Those tanks are to be used with this vapor separator tube that goes in the trunk. I’m trying to figure this out as well. I’m going to reuse mine but not sure what to do with the 5th line that is supposed to go to the valve cover breather/pcv valve. I won’t be RJ. King stock valve covers. I’m thinking it could just vent to inside the frame rail.

IMG_7444.png


IMG_7524.png
 
67Dart273 said:
It breaks a siphon. ON a hot day, with the tank really full, the fuel can back clear up into the fill tube, especially parked on a hill AKA Seattle/ San Fran, and siphon out the vent onto the ground. With the "U" as soon as the fuel gets low enough it will pull air and stop. The fuel cannot flow out again, until it backs clear up to the top of the U level wise. If you are driving, you may use enough that it won't siphon again, or if cooling towards the end of day, the fuel may subside on it's own.

If you can silver braze or conventional braze, or even gas weld, you could braze a fitting into the neck On a car where the neck goes in from the outside, you need to keep the fitting fairly flush so it will clear the fender hole
Click to expand...
The 71 has the filler neck being installed from inside the car. I may try to weld a 1/4in diameter nipple to the upper part of the filler neck (filler neck not currently installed). Then I can use 1/4in fuel line to make the U shape and run the vent line down the filler neck, through the floor, then stuff the end in the closest section of frame rail.
 
str12-340 said:
I'm curious - the factory tanks with 4 nipples had a "tank inside the tank" maybe a gallon or so in capacity. - part of the emissions system. Does your tank have that? I can't figure out how the 4 nipples work without that and those tanks had a rubber plug in the top of the tank to drain that little tank. I don't see that plug on on yours...
Click to expand...
I won’t be using the 4 ports on the tank. They came plugged when I got the tank, I’ll vent it another way
 
So far as the early 4 port with vapor separator, I do not believe you can use those ports WITHOUT a vapor separator. They are below fuel level, with fuel up in the filler at all. That means there is no way to break the siphon.

Also you hear guys suggest using a vented cap. I am against that. With no tank vent, but a vented cap, if you ever get into a situation, quite full tank, maybe parked with pass. side "down" a little bit and a hot day, you will have fuel all over the quarter panel
 
67Dart273 said:
So far as the early 4 port with vapor separator, I do not believe you can use those ports WITHOUT a vapor separator. They are below fuel level, with fuel up in the filler at all. That means there is no way to break the siphon.

Also you hear guys suggest using a vented cap. I am against that. With no tank vent, but a vented cap, if you ever get into a situation, quite full tank, maybe parked with pass. side "down" a little bit and a hot day, you will have fuel all over the quarter panel
Click to expand...
That’s what I was wondering, I would prefer to use one of the ports as the vent, but they are below fuel level and I want to be able to fill the tank up all the way and not have to worry about it
 
So easy, a caveman can do it. Post #3 is the best way.
Get the filler tube from a 67-70 Dart.
 
Ending up following the advice of post #3

I drilled into the filler neck and threaded in a 1/4in fuel line fitting. Used 1/4in fuel line and looped it up into the quarter panel, tied it to the fuel filler neck then through the trunk floor gasket and into the frame rail. I’ll try and post some pics tomorrow
 
Evan Dutch said:
Ending up following the advice of post #3

I drilled into the filler neck and threaded in a 1/4in fuel line fitting. Used 1/4in fuel line and looped it up into the quarter panel, tied it to the fuel filler neck then through the trunk floor gasket and into the frame rail. I’ll try and post some pics tomorrow
Click to expand...
What did you do with the other four ports on the actual tank. I have that style tank with the 5 port vent tube. Was going to reuse it but not sure what to do with the line that is supposed to go to the breather in the valve cover. Wondering if I should go the route you did or keep what I have.
 
Moparone said:
What did you do with the other four ports on the actual tank. I have that style tank with the 5 port vent tube. Was going to reuse it but not sure what to do with the line that is supposed to go to the breather in the valve cover. Wondering if I should go the route you did or keep what I have.
Click to expand...
Those ports came capped off, I left them that way
 
remember that you will probably never look at them again (out of sight, out of mind) so a high quality cap, or even a piece of gas hose with a bolt screwed in with proper clamps. You never want a gas leak there
 
Tape an M-80 to the side and light it...

The tank will be vented...
 
Evan Dutch said:
Hey guys,

I’m getting around to finishing the fuel system of my 1971 Plymouth Scamp. My new fuel filler neck is not vented and I’m running a new tank like the one pictured. This car is EFI, the pump is mounted outside of the tank.

What would be the best way to vent this setup? Could I utilize one of the 4 ports that are circled in the pic? Or is there a better way?

Thanks,

Evan

View attachment 1716175099
Click to expand...


There should be 4 hoses already in the rear of your '71 that those ports attach to...

There was on our 71 Valiant...
 
Read up on the how-and-why of that '70-'71 4-port tank setup here. Then vent your tank with a charcoal can (info in link) unless you like smelling gasoline wherever the car is parked.
 
Evan Dutch said:
I have a new fuel neck in the box so I’ll use the one for a 1971 scamp. Did you make your hose into a U shape like the factory pipe? Also, whenever the hose exits the floor where Did you ultimately run it to?

Did you have any issues with threading your fitting into the filler neck? The tubing wall of the filler neck should be thick enough to accept a tap right?
Click to expand...
The reason I drill a small hole and forced a tapered punch in was tofold the metal inward for material for the pipe tap to force the threads outward. All I used was a 90 fitting on the top and ran the line down to the underside of the floor . Exactly what the factory did for 67-70 cars with the metal tube. I may have a 70 dart tube but I do not have a cap to go with it..

71's have a vented cap but with my fuel consumption I wanted to make sure I had a big enough vent system.
 
While your system will work, sorry but it is janky at best.

When I mentioned post #3, this is what I meant.

For $20-$30 Why not do it right ?

1701917794522.png
 
slantsixdan said:
Read up on the how-and-why of that '70-'71 4-port tank setup here. Then vent your tank with a charcoal can (info in link) unless you like smelling gasoline wherever the car is parked.
Click to expand...
CHRIST here we go AGAIN. The 69/ pre evap systems worked just fine AND DID NOT SMELL in the garage any worse than your uber green "carbon(sh*t) can"
 
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