Suggestions on venting fuel tank

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C2ndLTpigeon

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I have a 1973 Plymouth Valiant 318, I am not longer running a Charcoal canister any more since the car is not longer stock. I have since plugged the single vent nipple on the fuel tank. I have a feeling that his is not allowing me to fill my tank up to the max. My gauge is barley at the full but it used to be able to go past the last dash and stay there for a bit. I have taken the filler neck out and noted the level and its the the bottom of the filler neck seal leaving a little bit of tank that can be filled past the filler neck.

Anyway, the only thing I have venting the tank is a vented cap. Ive seen some posts about a 69 Dart filler neck that has a vent that goes down the neck past the trunk floor boot to outside air. Is that a good route to go? Or is there some other ways?

Thanks!
 
If your gas tank only has one vent fitting- I believe you have the wrong tank, at least not the original. Since you are removing most of the smog crap you now have the correct tank. I would vent it as original. going up the filler to form a loop, and then down the filler to under the car so you don't smell the fumes.
 
Get a vented cap.

Already have a vented cap. Some past posts mention thats not the best way to vent the tank?

My other issue like stated above is not being able to fill the tank to the max, I am in CA were we have those stupid vapor pump nozzles so it spits fuel out when it "says its full but I think it can really take another gallon and push it past the full like it used to. Is having the tank vent plugged contributing to this?
 
If your gas tank only has one vent fitting- I believe you have the wrong tank, at least not the original. Since you are removing most of the smog crap you now have the correct tank. I would vent it as original. going up the filler to form a loop, and then down the filler to under the car so you don't smell the fumes.

I recently replaced the tank, but it is a match to the one that was on the car when I bought it. It looks like it was the original tank but I could be wrong. It has the same single vent at the top the ran a small rubber line to a hard line that ran to the front and went to the charcoal canister and to the old carb.

What was "original" what would I need to add or change?

Thanks
 
Already have a vented cap. Some past posts mention thats not the best way to vent the tank?

My other issue like stated above is not being able to fill the tank to the max, I am in CA were we have those stupid vapor pump nozzles so it spits fuel out when it "says its full but I think it can really take another gallon and push it past the full like it used to. Is having the tank vent plugged contributing to this?

It could well be. Have you tried filling the tank the rest of the way with the nozzle backed out a little?
 
Already have a vented cap. Some past posts mention thats not the best way to vent the tank?

My other issue like stated above is not being able to fill the tank to the max, I am in CA were we have those stupid vapor pump nozzles so it spits fuel out when it "says its full but I think it can really take another gallon and push it past the full like it used to. Is having the tank vent plugged contributing to this?

....and I don't care what "some posts" or "other people" say......I always do what's best, easiest and most affordable for ME for the given situation. JMO.
 
I have a 73 also , what I did is take the hose and place it on the inner fender well, higher than the gas tank and put a one way valve on the end and used a zip tie to hold it. That way air can go in and nothing can come out. This is the valve you can blow in one end but not the other, so place it so the gas cannot get out but air can get in .

IMG_20201114_094601817.jpg
 
..............................Sigh................................

OP: Suggest you go over to MyMopar and download a free 73 service manual, and read and find out how the vent originally worked

Then download a 69 manual and find out how THOSE worked.

Then download a 70-71 manual and not the differences between those and your 73.

You say you have a "vented" cap. Are you sure? Or do you have the factory "pressure vacuum" cap which is NOT truly vented, but rather for pressure relief under both pressure and vacuum.

You can pull the cap immediately after a drive and see if there is vacuum in the tank

Be careful. The easiest way, if the smog stuff was intact, would be to leave the original 1/4" vent going up to the engine bay "open" up HIGH in the bay to prevent siphon. Others have suggested plumbing that line into the air filter bonnet to prevent smell.

By removing/ plugging "stuff" you can easily end up with a non-vent situation.

I DO NOT LIKE VENTED CAPS!!! The 69/ earlier were sealed, and the vent in the filler worked GREAT

The tank vent DOES NOT HAVE anything to do with filling the tank. That is done by the baffle in the filler tube.
 
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My suggestion.

Vent the tank properly. Vented gas cap, vented filler tube, etc.
Never fill the tank to the top.
Rarely will my tank be filled past 1/4 -1/2 full.
 
I have a 73 also , what I did is take the hose and place it on the inner fender well, higher than the gas tank and put a one way valve on the end and used a zip tie to hold it. That way air can go in and nothing can come out. This is the valve you can blow in one end but not the other, so place it so the gas cannot get out but air can get in .

View attachment 1715629972

How will that work as a vent when a vent is to let air OUT of the system?
 
The 69/ earlier were sealed, and the vent in the filler worked GREAT

That's the way my 64 is and it works just fine. I would recommend he do something similar, but that puts him brazing on the gas filler tube. As Beaver Cleaver would say, "I'm not sponsible"
 
Not sure if a '67/'69 Dart filler neck is the same. Mega Parts has the filler neck and vent tube for $70. The rubber floor piece is $25. I have the filler tube in my '69 DART, I had to massage the vent tube some.
Maybe some else knows if the parts will cross.
 
The 69 is not the same. Different shape, and the early ones (the flange) go in INSIDE the trunk, where the flange on the later ones are outside. But you could pull that one and modify it. What "I guess" you'd have to do is braze/ silver solder something like a shortened 1/8X 1/4 NPT bushing into the filler, as flush as you can on the outside, shortened so the nozzle won't interfere on the inside. Keep that in mind when placing the fitting. This is because the tube comes in the side from the outside, a 69 style tube will not clear the flange

I have a 74. I have thought about brazing a tube in "flat" against the filler and then sawing a small notch in the quarter panel hole flange to allow passage, then bend the tube out slightly to get a hose fitted
 
Do I have my filler neck in from the wrong side? My flange is on the inside of the trunk. '69 Dart
 
I am thinking it could go either way, I just put it back in the way it came out. If it will go in from the outside, it would answer why I had to modify my new painted cap.
Someone said that the new 1/4 panels gas cap recess had a wrong radius and that was why my cap had to be modified.
I would like to know.
 
Do I have my filler neck in from the wrong side? My flange is on the inside of the trunk. '69 Dart

No. Early ones with the vent tube in the neck will not go through the hole. So the flange end has to be inside.
 
..............................Sigh................................

OP: Suggest you go over to MyMopar and download a free 73 service manual, and read and find out how the vent originally worked

Then download a 69 manual and find out how THOSE worked.

Then download a 70-71 manual and not the differences between those and your 73.

You say you have a "vented" cap. Are you sure? Or do you have the factory "pressure vacuum" cap which is NOT truly vented, but rather for pressure relief under both pressure and vacuum.

You can pull the cap immediately after a drive and see if there is vacuum in the tank

Be careful. The easiest way, if the smog stuff was intact, would be to leave the original 1/4" vent going up to the engine bay "open" up HIGH in the bay to prevent siphon. Others have suggested plumbing that line into the air filter bonnet to prevent smell.

By removing/ plugging "stuff" you can easily end up with a non-vent situation.

I DO NOT LIKE VENTED CAPS!!! The 69/ earlier were sealed, and the vent in the filler worked GREAT

The tank vent DOES NOT HAVE anything to do with filling the tank. That is done by the baffle in the filler tube.

I still have the original line hard line on the car, all I would need to do is put a piece of fuel line and connect it to the hard line from the rear to the tank nipple, as you mentioned this would let it vent to the the front of the engine where the line originally connected to the charcoal canister. If it vents this way is it save to have it went to atmosphere under the hood? Should I be worried about fumes near a hot engine?

Thanks.
 
I still have the original line hard line on the car, all I would need to do is put a piece of fuel line and connect it to the hard line from the rear to the tank nipple, as you mentioned this would let it vent to the the front of the engine where the line originally connected to the charcoal canister. If it vents this way is it save to have it went to atmosphere under the hood? Should I be worried about fumes near a hot engine?

Thanks.

You could even hook the charcoal canister back up. It has some benefits.
 
Dollars to donuts your sending unit is not stock, and thats your problem

Also, put the charcoal cannister back on, it actually does something useful without robbing power
 
Dollars to donuts your sending unit is not stock, and thats your problem

Also, put the charcoal cannister back on, it actually does something useful without robbing power

Sending unit is not stuck, Ive dropped that tank about a dozen times in a weeks period.

Pulled the canister off since 2 of the inlets on the top were broken off when I got the car and it made an excellent spot for me to put my Vacuum canister for my power brakes since my cam produces low Vac.
 
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