Is there a alternative to the factory fuel tank venting system on my 70 RR?

[70 RR]

I have had problems with fuel escaping from my vent lines when l come to a stop with 10 or more gallons of fuel in my tank. I removed the factory vent lines and attempted to reinvent the wheel but l still have the same problem. This is dangerous and expensive, can anyone help? Pictures of a better setup would be much appreciated. Thanks!

 

[slepr1]

Cap them and get a vented fuel cap (or drill a small hole in it for venting).

 

[440roadrunner]

Cap them and get a vented fuel cap (or drill a small hole in it for venting).

As low and "to the rear" as the filler is, seems to me you'd have a constant leak back there at the cap.

70RR was yours originally with or without the CA evap controls, that is, a carbon can, and the extra separator can in the trunk? Was that ever there, still in place or been removed?

In 70 non CA cars did not have the evap system (mine did not) and so there are differences.

You have a factory shop manual? Download one over at MyMopar

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

What you want is in chapter 9A as well as 14

You say fuel comes out, braking..........It's been decades since I owned mine, but that never happened Without the evap system "as built" my car had no lines up front except main fuel and the vapor return from the pump can

Below are the two different situations "you can have" in 70. The top photo is 70 WITHOUT the evap system, a non CA car. The secret to "how these work" is that the vent line is attached to a point on the tank that will be "above gas" and goes up "fairly high" in the car, so that suction (siphon) will be broken.

These cares will only have one or two tubes to the front of the car, depending on whether it has the vapor return (440 -426)

The bottom photo shows a CA car with the evap system, and the key here is the additional vapor separator and extra tubes. If this setup is a 440-426 with the vapor return, it will have THREE tubes to the front

If you have this setup, one key is to get all the tubes "wired" correctly. The vent going to the front MUST be the tube which goes to the top of the separator, the purpose of which is to drain back fuel to the tank.

 

[70 RR]

Mine did not have the can. I had the line that went up into the trunk and then back down again. The line coming back down didn't lead to anything in particular, just stopped.

- - - Updated - - -

Cap them and get a vented fuel cap (or drill a small hole in it for venting).

I was thinking it would then leak through the cap, am l wrong?

 

[440roadrunner]

Mine did not have the can. I had the line that went up into the trunk and then back down again. The line coming back down didn't lead to anything in particular, just stopped.

- - - Updated - - -

I was thinking it would then leak through the cap, am l wrong?

So what do you have on it now for a vent? The fact that the factory one went "up high" and then came down "and stopped" is what makes it work. It causes the thing to break suction. Is this an OEM tube, or something someone made? That is, was it installed correctly, maybe, ends too low?

How about the tank itself? Is it original or repop, or what? Maybe you have "the wrong fitting" IE does it have unused fittings?

The "A" bodies run the line down into the interior of the rear frame and then stop there

As I said earlier, I think a vented cap would cause a constant mess at the filler

 

[70 RR]

I agree with you on the vented cap. Currently l have some lines coming off of the tank but the aren't going high enough to break the auction. I am going to have to try and rework the system or go back to factory setup.

 

[bigmanjbmopar]

On my 69 I looked inside the tank with a bore scope and discovered the replacement tank had the lines reversed from the factory set up so I switched them and then drilled two 1/8" holes in the non-vented cap and now it all works like it's supposed to. You can smell it on hot days occasionally but it does not leak out on the ground anymore.

The factory vent lines are one shot and one long, on the outside and inside. The short one goes all the way back to the filler neck inside the tank, it's for when you are in a incline the tube would be exposed and can vent out fumes, the long tube that goes through the trunk is a short tube on the inside of the tank and is for when you are in a decline, both will work when less than full.

I would first blow out the factory vent lines with compressed air to see if they are clogged at all. If not re install them but in reveres on the tank and drill the holes in the cap.

 

[440roadrunner]

On my 69 I looked inside the tank with a bore scope and discovered the replacement tank had the lines reversed from the factory set up so I switched them and then drilled two 1/8" holes in the non-vented cap and now it all works like it's supposed to. You can smell it on hot days occasionally but it does not leak out on the ground anymore.

I can understand if something was built wrongly, but WHY would you need to vent the cap? I've owned a 69 and a 70, and the vent system worked just fine. Under hard acceleration, fuel would be forced "forcibly" against the cap, and they WILL leak, or at least "make icky crusty mess" if the cap is un-sealed.

So I guess my question is, after you went to all that trouble (and took that photo) why did you feel the need to vent the cap?

 

[Yatzee]

I recently installed a custom made aluminum tank which required not only a vent valve but one that acted as a rollover anti-siphon valve as well. Although the vent nipples on your tank are 1/4 or 5/16 they can be up-sized for various check valves with reversed reducers. Some vents come out in the wheel well up high and some above the rear axle. These have been around a long time and can be purchased in a lot of places. Under no circumstances drill a hole in the cap if the fill tube is low and at the rear.

http://atlinc.com/fill-necks-fill-caps-vent-valves.html

http://www.racereadyproducts.com/fuel-cells--accessories/fuel-vent-check-valves/

 

[kiwigtx]

Nice write-up and pictures Bigman. :headbang:
I had a small leak a few years ago, and found that the soldered joints around the vent lines on the outside of the tank had small fractures. I had the local radiator shop re-solder the pipes, and all works well now. :icon_thumright:

 

[Dennis H]

Good info here. Make sure that the forward upper vent line in the diagram is routed HIGH enough. Mine goes almost to the rear shelf. Problem solved. It is easy to forget that some aromas are normal for cars this vintage. A mild hint of raw fuel under certain conditions - like parking nose-down after a fill up etc.

 

[70 RR]

Ok, all of this info is great but l no longer have the original factory lines in place and need to know if l can fabricate some lines that will do the trick.

What l am wondering is, if the whole point of the longer tube that goes up into the trunk is to elevate to a level higher then the top of the tank, why can't l just drill a couple of holes directly above the inner most vent into the trunk and run my vent tube up into the trunk, bend it 180 degrees and back through the floor and pointing at the ground. The outer most vent could have a tube that is simply shaped like a cane going up toward the trunk and hooked at the end and back down. Am l crazy to think this would work? It seemed that the factory line was way over-engineered.

 

[383man]

Some of the early 70 Mopars had the factory emission system that vented the gas tank to the valve cover breather but I guess yours did not. I know some cars ran a vent line up high and then back down and then inside a frame rail. I use a vented cap on my stock 63 tank which is how it was from the factory and it works good but if I race it or get on it hard with more then half a tank I can smell gas fumes at the gas tank cap behind my tag. Its not bad and I live with it but I would do as you want and make a vent tube run up high in the trunk and then back down low under the car as that should work fine. You dont want to loop the vent line in any way where fuel could sit in the line and block it from venting. I take it your tank has a vent line coming off the tank as it would be nice if you had a newer tank that used a vent/roll over valve that they used with charcoal canisters systems as they work nice for venting. Ron

 

[440roadrunner]

make a vent tube run up high in the trunk and then back down low

Be careful not to run it too low. Been along time since Ive had a B. I think mine ended "up high" there in the hump above the rear axle. You do not want to bring it down below the tank or it can siphon.

 

[383man]

Be careful not to run it too low. Been along time since Ive had a B. I think mine ended "up high" there in the hump above the rear axle. You do not want to bring it down below the tank or it can siphon.

Thats right as I just meant to bring it back out of the trunk and under the car and maybe into a frame rail as I have seen before. Ron

 

[TetanusShot]

As a reference, I vented mine up to the top of the hump above the axle. It's as high as you can go without drilling a hole. When the tank is full or even near full, the fumes build pressure in the tank and push fuel out the vent even though its well above the tank.

'70 Road Runner, not a California car.