Gas Tank Vent

[straightlinespeed]

The other thread that about the 71 Demon vent line has me thinking. My car was also a CA emissions car and the same line was capped on my car. I installed a new fuel line and removed that vent line.

Out of the tank there were also 4 other lines that went to that aluminum tube inside my trunk. I plugged all but 1 of those lines and ran a rubber hose from the tank to one of those tubes. My thinking is I could use that for the vent line. Will that work, or needed? I have a vented cap.

 

[67Dart273]

You must have a 74/ later car?

What makes you think you have a vented cap. NO A body every used a truly "vented" cap. The later ones were "pressure vacuum"

Using a vented cap only invites fuel slopped all over the side of the car.

Without a diagram of what you did to the vent lines, no way of knowing. If you leave the tank hooked to the trunk gear "as advertised" then run an open tube from the original line which had gone up front, and ran that "up high" and back down, that should be OK.

The BEST way in my opinion, is to braze/ weld a vent line into the filler tube exactly like the 67-69 and some 70 cars did.

 

[moparman3406bbl]

It's a 71 california emmissions spec my 71 has it also never changed it why would you you can get a new tank for just over 125.00 if you need one

 

[straightlinespeed]

You must have a 74/ later car?

What makes you think you have a vented cap. NO A body every used a truly "vented" cap. The later ones were "pressure vacuum"

Using a vented cap only invites fuel slopped all over the side of the car.

Without a diagram of what you did to the vent lines, no way of knowing. If you leave the tank hooked to the trunk gear "as advertised" then run an open tube from the original line which had gone up front, and ran that "up high" and back down, that should be OK.

The BEST way in my opinion, is to braze/ weld a vent line into the filler tube exactly like the 67-69 and some 70 cars did.

Actually my car is a 71 Scamp. Since I could not find a 71 fuel cap I replaced the fill tube with a 76 filler tube. Since the caps are easier to get. I assumed it was vented, not 100% sure though.

There are 4 lines coming out of the tank and 5 lines in that aluminum tube thats in the trunk. I just picked one, but I could blow air thru them to see if any of them are connected. I have no idea how the lines are run inside that tube.

 

[straightlinespeed]

It's a 71 california emmissions spec my 71 has it also never changed it why would you you can get a new tank for just over 125.00 if you need one

Because I never had a 71 gas cap, and wasnt about to pay $80 or up for a cap and Im not running any emissions. Actually when I bought the car everything was disconnected on it. So since I swapped a engine and repainted it I figure get rid of the stuff that was not being used.

 

[67Dart273]

Look at the diagram in the thread. I BELIEVE the vent which originally went up front is in the TOP of the vent tube, and the ones going to the tank are in the BOTTOM. This allows the vent to be "above fuel" and allows any slopover to drain back to the tank. So I believe it's important to tie into the original front line.

Sounds to me like you likely have a pressure / vacuum cap. It should be rather deep and clumsy, and appear to have a valve inside.

The 69's and earlier, and some 70 (no CA) all used sealed caps

http://www.forabodiesonly.com/mopar/showthread.php?t=183956

Pressure vacuum cap in this thread

http://www.forabodiesonly.com/mopar/showthread.php?t=202184

 

[straightlinespeed]

Look at the diagram in the thread. I BELIEVE the vent which originally went up front is in the TOP of the vent tube, and the ones going to the tank are in the BOTTOM. This allows the vent to be "above fuel" and allows any slopover to drain back to the tank. So I believe it's important to tie into the original front line.

Sounds to me like you likely have a pressure / vacuum cap. It should be rather deep and clumsy, and appear to have a valve inside.

The 69's and earlier, and some 70 (no CA) all used sealed caps

http://www.forabodiesonly.com/mopar/showthread.php?t=183956

Pressure vacuum cap in this thread

http://www.forabodiesonly.com/mopar/showthread.php?t=202184

Thanks that diagram does help. Although there is no way to see inside that tube so its hard to tell which one was the vent line. I believe I know which one it is but with out the car being near me I have to remember to do this. Also thanks for the link explaining the cap to me.

 

[67Dart273]

I'd bet that if we look in the 72 shop manual, it will tell ya

Here:

[ame]http://www.abodyjoe.com/pictures/Misc.%20car%20info/1972%20Plymouth%20Chassis%20Serv%20Man.pdf[/ame]

Here's a 71 manual, but it's "body only" no engine, electrical, etc

[ame]http://www.abodyjoe.com/pictures/Misc.%20car%20info/71DodgeBodyManual.pdf[/ame]

Well, heh, didn't see it in the 72 manual, so I checked the 70 manual from MyMopar

http://www.mymopar.com/index.php?pid=31

The link

http://www.mymopar.com/downloads/servicemanuals/1970_Plymouth_Service_Manual.zip

Page 672. (This manual does not use the proper "dash" numbering)

Does this look like yours?

 

[straightlinespeed]

Yep it does! If I see that correctly I would you the line closest to the front of the car.

Also, I've thought of something else.. Does the 76 filler tube flange mount inside the trunk? I installed it on the outside and that was because that is where the gasket was stuck on it... If it should be inside the trunk I will have to drop the tank because the tube is so damn long compared to my 71

 

[67Dart273]

Sorry, don't know about in/ out. My 67 is inside

 

[straightlinespeed]

So was the neck on my 71.

Anyways, back to the vent line. The line, labeled vacuum line, is that the one that sucked the vapors back into the carb to be burned? On the page prior to that 671(sorry I dont know how to get a PDF picture). They show the tubes inside the canister in the trunk. The one going to the breather on the engine is what Im considering the vacuum line. So Im assuming that I should connect any of the 4 lines from the fuel tank to that one since its the highest one in that canister?

 

[67Dart273]

Not sure how to answer that. The reason for 4 lines going to the tank in the trunk was to do exactly what it's called --a liquid vapor separator. The idea behind the 4 lines out of the tank was that at any given time at least one of those lines would be open ---above liquid.

THAT is the vent so far, at the time.

So the "vent", goes up into the vapor separator, where any fuel "slop" can drain back into the tank, then the vent goes up front.

It doesn't really NEED vacuum on it, is simply needs to be OPEN

So if you are eliminating the carbon can system, you need to replace the "up front" line with "something" that goes up high in the car (clear to the top of the trunk) then back down and out through the trunk floor --left open.

If you look at the diagram on one of those threads of the pre--70 vent system, they essentially use the fuel filler tube for a "liquid vapor separator" by cutting the vent line into the filler "nice and high," running the tube as high as possible in the rear quarter, then finally, back down along the filler, through the trunk floor (gasket) and simply open - ended in the rear frame rail.

The whole deal is, you need some way of guaranteeing that do not start a siphon. Let's say, you eliminate the vapor separator, and plug all the tank lines except one. Let's say you run that line up high, and back down, open, below. There might just come a time when.................

you park with that side "down" on a sidehill...........

A nice hot day expands a full tank of fuel..............

and a siphon starts, and when you get to the car, you either have police and fire, a smouldering pile, or at least, not much fuel left.

Now, the OLDER system, with the vent in the filler tube can ALSO siphon under extremes, IE the tank very full, but the MOST it can siphon, is maybe a cup? or so, before the fuel gets below the filler tube vent tube connection. As soon as the level goes below that, the siphon breaks.

 

[straightlinespeed]

Ok, I understand what your saying.

That vacuum line that ran all the way to the engine bay was eliminated and was capped off. Hence why I pulled that line out. The charcoal canister and any of the other emissions stuff was also eliminated. The only thing hooked up when I started swapping was the 4 lines from the tank to the 4 lines to the trunk canister. I did not have any issues prior except for vapor lock. I dont know if that was related or not..

I could easily hook up the 4 lines again and then leave that one line that was connected to the vacuum line open and that I suppose would act like the vent line.. Well in my thoughts, but I could be mistaken..

Thanks again for talking this thru with me.