Gas tank venting

hdfx81 · #1 (**permalink**) 05-20-2008, 06:19 AM

Hi Everyone
I just replaced the gas tank in my 73 bronco,on the one I removed the two vent lines(for charcoal canaster?) were blocked off and when I took off the gas cap you could hear suction

. My question is, on the new tank should I leave at least one of the vent lines open?

Will I create vapor lock if I don't?

Thanks,Mike

Boba Fett · #2 (**permalink**) 05-20-2008, 05:56 PM

The gas pump might want to shut off all the time. You can't leave one open because then the tank will leak gas when full. Easy way is to plug them both. I did that, but the gas pump wont stay on when filling up. The best thing to do would be to retrofit in a modern emissions system.....

McLeod · #3 (**permalink**) 05-20-2008, 08:36 PM

If the vent ports on tank are plugged, I believe you must use an earlier pre emissions vented gas cap.
If your cap is air tight, you need to have some other way to vent the tank.
66-70 use a different cap than 71-77.

I say plug both ports on tank and go with vented cap if you don't have emission inspections.
Otherwise, you probably aught to restore the charcoal canister venting system.

JCastellaw · #4 (**permalink**) 05-22-2008, 04:47 PM

I have a polyurethene tank that I am cleaning. it came from jeff's years ago and has two either 1/2 or 3/8's holes for vents? I am not sure if I should plug both of them or not. Why two small holes???

EricJ · #5 (**permalink**) 05-22-2008, 05:39 PM

Quote:

Originally Posted by JCastellaw

I have a polyurethene tank that I am cleaning. it came from jeff's years ago and has two either 1/2 or 3/8's holes for vents? I am not sure if I should plug both of them or not. Why two small holes???

I'd go with McCleod, use a vented cap or it will try to crush the tank with vacuum.

JCastellaw · #6 (**permalink**) 05-22-2008, 05:43 PM

Where can you get a vented cap??
Is it hard to get fuel on your tank????

EricJ · #7 (**permalink**) 05-22-2008, 05:51 PM

Quote:

Originally Posted by JCastellaw

Where can you get a vented cap??
Is it hard to get fuel on your tank????

My 65 pickup has the vented cap, so you can use that to look it up. As far as filling it with fuel it's a crap shoot, you'll have to try it and see how it does. IF it keeps backing up you'll have to vent it somewhere. If you need to vent it, run a line up under the hood and put an inline fuel filter on the end to keep bugs and debris out, and attach it high on the fender well or firewall.

McLeod · #8 (**permalink**) 05-22-2008, 08:34 PM

Quote:

Originally Posted by JCastellaw

Where can you get a vented cap??
Is it hard to get fuel on your tank????

This is the pre emission one:
Gas Cap, Chrome 66-70

This is non-vented one:
Gas Cap, Chrome 71-76

I have that same poly ethylene tank. What a piece of junk. When I fill it up the weight of the fuel makes the tank sag around the strap.
Maybe I'm not suppose to use the factory mounting strap with it

I think I'm going to get the 23 gallon steel tank.

If I remember correctly (I'm not in garage at moment) my fuel filler neck (that came out of a 73) had a small hose that connected the tank with the upper end of the filler neck which would prevent the fuel from backing up while filling. See here:
Vent Hose, Rear Tank, 66-77

The other port got plugged.

Regards
Ken

NumberDummy · #9 (**permalink**) 05-22-2008, 08:46 PM

B6TZ-9030-A .. Gas Cap-Vented Anti-Surge-Chrome Finish (Motorcraft FC-23)

Fits: 1953/72 F100/1100's / 1966/70 Bronco's.

Not used with evaporative emission control.