During deceleration, fuel dumping out of the tanks vent line. What gives?

[1 Wild R/T]

Typically the vents I have seen don't go into the tank but screwed to a fitting on the high side of the tank. Hope that makes sense..

But is that thread bung just an open ended bung? Or is there a fitting threaded to the inside of the bung that goes to the very highest point in the tank...

 

[1 Wild R/T]

Float levels are at the half way point in the bowl window.

If the carb floats were high the engine would flood, not pour fuel out of a tank vent...

 

[fullmetaljacket]

Vent tube is on the high side of the tank.

 

[QuickBpBp]

But is that thread bung just an open ended bung? Or is there a fitting threaded to the inside of the bung that goes to the very highest point in the tank...

While I have not seen his tank it's typically just a bung on the highest point with nothing on the inside...

 

[QuickBpBp]

I don't think I saw this answered is this a new set-up or an old one that just started doing this?

 

[1 Wild R/T]

Vent tube is on the high side of the tank.

Someone's been putting fuel in your car a night trying to trick you into thinking you've got an economy car that creates fuel....????

Seriously though it's pressurizing the tank but the pressure should vent through the vent & being the highest point it should vent vapors not fuel... So what happened inside the tank to lower the vent point...

 

[1 Wild R/T]

I don't think I saw this answered is this a new set-up or an old one that just started doing this?

He stated it's an old system that's been fine until recently..

 

[QuickBpBp]

Does the vent have a roll over valve inline with the vent that might be acting up closing off the vent?

 

[1 Wild R/T]

Does the vent have a roll over valve inline with the vent that might be acting up closing off the vent?

If that were the case the fuel wouldn't come out.... I really think either it needs a vented fuel cap or something about the vent has changed inside the tank...

 

[fullmetaljacket]

Does the vent have a roll over valve inline with the vent that might be acting up closing off the vent?

It's a coil roll over vent. I'm gonna remove the vent and check it for any foreign matter in it. Then again as Wild RT mentioned, the fuel would not come out if there were a clog.

 

[QuickBpBp]

If that were the case the fuel wouldn't come out.... I really think either it needs a vented fuel cap or something about the vent has changed inside the tank...

I don't know enough about the design but if it's acting up and closing say while driving, building pressure then when stopping is opening again... Just thinking out loud and I don't know if his tank has one..

 

[QuickBpBp]

It's a coil roll over vent. I'm gonna remove the vent and check it for any foreign matter in it. Then again as Wild RT mentioned, the fuel would not come out if there were a clog.

Ok so nothing on the other side of the bung.. and if it was clogged it sounds like it got a good flushing..

 

[1 Wild R/T]

Let us know what you find... Certainly a weird one...

 

[Daves69]

It's a coil roll over vent.

With a check ball in line?

 

[QuickBpBp]

It's a coil roll over vent. I'm gonna remove the vent and check it for any foreign matter in it. Then again as Wild RT mentioned, the fuel would not come out if there were a clog.

Last question then you will have to let us know.. Is this a braided line coiled vent like this one?

Fuel Cell Vent Kit -8an Rollover Valve Vent Kit | eBay

Or is it like my vent I have on my fuel cell which is 1/2 inch aluminum line coiled? If it's the braided line maybe the line inside collapsing allowing it to build enough pressure before it blows it open and can collapse again. Kind of like how rubber brake hoses go bad but look fine on the outside...

GOOD LUCK and report back when it's fixed!

 

[1 Wild R/T]

@fullmetaljacket
Just had a thought, do the coils of the vent stand up or lay on their side? If they are standing up they can act as a one way check...Pull the gas cap and blow compressed air through the vent line.. It could be fuel is trapped at the bottom of each coil not allowing the vent to work... Re-position the vent so it lays on it's side & creates a constantly climbing spiral so any fluid drains back into the tank..

 

[mrmolding]

I had a friend back east who had a car shop tucked in his back yard (since closed down). He would spend time retrofitting older cars with mid 70s solutions to open tank vents with OEM tank vent valves and carbon canisters. I remember he put in a corvette tank rollover valve in one 60s mustang by mounting it higher than the tank and then sent it to a carbon canister in the engine bay. In another case, he took a 70s tank vent from an ebody I think and used that on a 67 GTX maybe? I think that one just vented to a rollover valve. But, I'm talking 10-15 years ago so not sure.

Anyway, his main idea was to retrofit open vent tanks using mid-70s solutions as tank/rollover/ball vents and then either sending them to carbon canisters or just another open air vent -- the cool thing was the vette and ebody valves would prevent gas from spilling out and prevent too much gas during fill up because they are ball-type valves, but also vent the tank.

I thought he was a little nuts, but it seemed to really work. I remember my 68 GTX in my 20s would burp gas all day long if I overfilled it especially on hot days.
With all of the hills and canyons where I live now, I've been seriously tempted to try out his solution, but I just keep the tank at 1/2 full and enjoy the car.

Anyway, just sharing one person's solution to gas coming out of tanks. I can't confirm how well it worked long term or in normal use, but I thought it was a pretty interesting solution.

Here are the different valves (ball valves?), separators?, he used...

This is the one for the vette that he just mounted above the tank for the mustang:
70-74 Fuel Separator Vent Vapor Valve At Gas Tank

and I'm sure everyone knows or has seen these:

 

[mrmolding]

Wanted to share as this really started me thinking. Here is a FSM diagram of the ebody and I think 73-ish bbody separator in the pic above...

 

[mrmolding]

Last one, I bought one of these at Fall Fling a few years ago since I'd not seen one in years...

 

[sarjag]

Does your fuel tank have two vent lines like some of the OEM tanks (like 1969)? If so, one is short and one is long. My 1969 Roadrunner aftermarket tank had these reversed. The short one should vent through the long tube that routes through the trunk. The long one (that goes to the rear of the tank) vents under the car through a short tube. If these connections are reversed, fuel will dump out the short vent tube on deceleration.