Gas Tank Venting
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
Gas Tank Venting
My evap canister has long since been disconnected from the carb by P/O. I would like to figure out the best way to seal up this system, as it has all of the hoses open.
I have a gas cap that only allows air in, to relieve vacuum. It does not allow air out, to relieve pressure. I assume this is called a non-vented cap.
I looked at the part store, but cannot find a vented cap. Does anyone know how the cannister works? I cannot tell if it is open to the tank or there are some check valves in there.
If I seal the cannister, is there a pressure relief somewhere on the tank or in the system?
I have searched quite a bit, but don't much except to put on a vented cap. I think there is a lot of confusion on this subject as no one refers to what they are venting (i.e. letting air in or letting air out).
If anyone knows a source for vented caps, I would appreciate that as well.
Thanks,
I have a gas cap that only allows air in, to relieve vacuum. It does not allow air out, to relieve pressure. I assume this is called a non-vented cap.
I looked at the part store, but cannot find a vented cap. Does anyone know how the cannister works? I cannot tell if it is open to the tank or there are some check valves in there.
If I seal the cannister, is there a pressure relief somewhere on the tank or in the system?
I have searched quite a bit, but don't much except to put on a vented cap. I think there is a lot of confusion on this subject as no one refers to what they are venting (i.e. letting air in or letting air out).
If anyone knows a source for vented caps, I would appreciate that as well.
Thanks,
Drifting
Joined: Oct 2007
Posts: 1,458
Likes: 1
From: Collinsville MS
St. Jude Donor '08
My evap canister has been disconnected also from the engine. The line to the tank is still connected. I put vacuum plugs over the outlets that run to the carb and PVC and all the other emission stuff. Engine still runs fine. I dont have a vented cap on my car. Was going to do that but it works fine the way it is. my .02
Drifting
Joined: Oct 2007
Posts: 1,458
Likes: 1
From: Collinsville MS
St. Jude Donor '08
I havent noticed any problems. When I got the car, this is the way it was set up, except the emissions lines were plugged with dirt. I took it apart and cleaned it up and put it back on. I think the vent line from the tank still vents through the cleaner in the canister and releases pressure through the bottom drain. I'm not real sure if thats how this works but I do know that when its not broken, I dont try to fix it. It seems to run a little rich at times and I think thats mainly my carb, but at some point I may rerun the carb line to the canister and try that for awhile and see if anything improves. Most people just ****** the evap canister off and put on a vented cap and go.
Melting Slicks
Joined: Sep 2006
Posts: 2,815
Likes: 470
From: Wichita Kansas
When I got my '72, it seems the hoses from the canister were not hooked up where they should have been; the gas smell in the garage sent me on a search that let to that discovery. Anyways, I hooked them up....but soon I noticed that after driving for a while, when I removed the gas cap, it would jump right into my hands, lots of pressure. First I tried a vented gas cap; solved the pressure problem but still had the gas smell. I figured something was plugged up so I replaced the fuel separator on the gas tank, ran a new (rubber) line from the separator to a new vapor canister, changed back to a sealed gas cap, and have not had the gas tank pressure problem since. If I was still having that much pressure in the tank, I would do something about it, doesn't sound too safe, that's why I did what I did.
Safety Car
Joined: Oct 2004
Posts: 3,725
Likes: 5
From: Minnesota
The evap canister and lines are long gone on my 75. When I dropped the tank a while back to cut out the bladder I ran a short line that ends with a small fuel filter from a vent hookup on top of the tank.
