Author Topic: 66 fairlane custom fuel tank breather leak  (Read 511 times)

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Jb427

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66 fairlane custom fuel tank breather leak
« on: September 10, 2022, 10:44:24 PM »
I have a custom fuel tank in my 66 fairlane with a return style fuel system my tank breather line is 1/2" runs around 2 foot vertical then has a rollover/check valve then the line runs back to behind the number plate and vents through the hole of the stock location gas cap.

when my tank is around 3/4 full it will leak i have looked at a few things i thought the rollover valve may of been opening and closing creating suction but i don't think that is the cause
I think the exit location behind the number plate may be the cause?

I like to see what people think could be the problem or a solution

top left of tank is breather under the trunk catch is the breather outlet  these are old photos with out the lines.
« Last Edit: September 10, 2022, 10:50:36 PM by Jb427 »

machoneman

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Re: 66 fairlane custom fuel tank breather leak
« Reply #1 on: September 11, 2022, 07:47:43 AM »
You didn't exactly say where the leak occurs but a good guess is at the vent location by the license plate.  Most old Fords have a somewhat similar vent system but with the vent end on the left side (driver's). Your rear location and lack of height to the vent line is, with gas sloshing back on acceleration, likely the source. I'd try running a rubber line to the vent on the tank (to the left of the tank) raise the center of that line up a least 4"-5" above the top of the tank and then route the open end down thru the OEM Ford hole in the fender well (or drill a new one). Can rig a temporary setup with some zip-ties to experiment.

Had a similar issue with my California-built '70 Stang that had a weird and new at the time special gas tank & fitting on the tank's top that vented fumes to a small charcoal filter. Bypassed it with a similar setup mentioned above.   
Bob Maag

Jb427

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Re: 66 fairlane custom fuel tank breather leak
« Reply #2 on: September 11, 2022, 09:24:50 AM »
It is leaking out the vent exit there is a plate covering the old fuel fill hole in the body and the vent exits there.

The vent line is raised very close to 2 feet above the tank directly up and inside the panel under the rear window before it goes down along just behind the trunk quater cover then along the back of the trunk and exit horizontal behind the number plate

I almost think that the horizontal location and air flow behind the number plate may be helping it to suck the slosh close to 2 feet up. To me that is along way for fuel to slosh through a 1/2 inch line with out some kind.

Not sure if that makes sense.

Jb427

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Re: 66 fairlane custom fuel tank breather leak
« Reply #3 on: September 11, 2022, 08:41:04 PM »
here is pic's of breather line and exit

can see a minor leak that i just noticed in this photo that is a rollover vent the top
and a pic of the exit spot behind the number plate

Falcon67

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Re: 66 fairlane custom fuel tank breather leak
« Reply #4 on: September 12, 2022, 09:41:01 AM »
Every vent I have has a big loop in it.  Both the door car cell and the dragster. 

machoneman

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Re: 66 fairlane custom fuel tank breather leak
« Reply #5 on: September 12, 2022, 11:17:02 AM »
It is leaking out the vent exit there is a plate covering the old fuel fill hole in the body and the vent exits there.

The vent line is raised very close to 2 feet above the tank directly up and inside the panel under the rear window before it goes down along just behind the trunk quarter cover then along the back of the trunk and exit horizontal behind the number plate

I almost think that the horizontal location and air flow behind the number plate may be helping it to suck the slosh close to 2 feet up. To me that is along way for fuel to slosh through a 1/2 inch line with out some kind.

Not sure if that makes sense.
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Yes, the second post showing your long vertical vent line = no way fuel can creep up that line. I doubt air flow can extract any fuel either. Fix your rollover to ensure it is not leaking and I think your issue is resolved.
Bob Maag