Gas Cap seal fixed/charcoal cannister deletion?

[DirtDonk]

Hiss can also be coming out. Gotta' feel for it rather than use the word "hiss" I suppose. Could go either way.
A pressure buildup can be easily caused by just ambient heat expanding the gas inside an unvented tank. Normally a return line should not do it by itself, because theoretically less fuel is returning than going back in. So not a fuel buildup, but more likely a heat buildup.
Only takes a few degrees to get a result. Especially when the tank is more full.

You can easily evap it with factory parts. Better still are newer factory parts that mimic the '76 and '77 models. Those charcoal canisters, or ones very much like them, can still be bought because they were used up into the early nineties at least. Anything newer than that is likely too exotic for our uses and needs a computer to control them.
But anything from the late seventies to early nineties in the rectangular plastic tank of about a quart capacity should work if it's got two large ports and two small ports. Or a small and medium port.

Lots of discussions about it here, but basically any stock tank from '70 and up should have the vent tube fitting you can use. You can mount the new canister to the firewall and run a hose from your tank's vent to the small port on the canister. Then run one of the large ports over to the air cleaner housing. Leave the other large one open, or better still use one of the standard "mushroom caps" that were there originally to keep debris and moisture out of the canister.

If your '76 is original it should still have a steel main tank with one, or two small 1/4" or so fittings sticking out the side, just in front of the main filler neck opening. \
I'd be interested in seeing some pics of yours to see if any of the original stuff is still there. And whether it has one or two of the fittings.
Is there anything like a charcoal canister mounted either up on the passenger side firewall, or a metal can mounted to the passenger frame rail just under the footwell?

Paul

 

[kat]

Hiss can also be coming out. Gotta' feel for it rather than use the word "hiss" I suppose. Could go either way.
A pressure buildup can be easily caused by just ambient heat expanding the gas inside an unvented tank. Normally a return line should not do it by itself, because theoretically less fuel is returning than going back in. So not a fuel buildup, but more likely a heat buildup.
Only takes a few degrees to get a result. Especially when the tank is more full.

You can easily evap it with factory parts. Better still are newer factory parts that mimic the '76 and '77 models. Those charcoal canisters, or ones very much like them, can still be bought because they were used up into the early nineties at least. Anything newer than that is likely too exotic for our uses and needs a computer to control them.
But anything from the late seventies to early nineties in the rectangular plastic tank of about a quart capacity should work if it's got two large ports and two small ports. Or a small and medium port.

Lots of discussions about it here, but basically any stock tank from '70 and up should have the vent tube fitting you can use. You can mount the new canister to the firewall and run a hose from your tank's vent to the small port on the canister. Then run one of the large ports over to the air cleaner housing. Leave the other large one open, or better still use one of the standard "mushroom caps" that were there originally to keep debris and moisture out of the canister.

If your '76 is original it should still have a steel main tank with one, or two small 1/4" or so fittings sticking out the side, just in front of the main filler neck opening. \
I'd be interested in seeing some pics of yours to see if any of the original stuff is still there. And whether it has one or two of the fittings.
Is there anything like a charcoal canister mounted either up on the passenger side firewall, or a metal can mounted to the passenger frame rail just under the footwell?

Paul

Thanks for all the info, gives me a lot to research. I will crawl under it next day or two to see what is there and what is not. I can say there is no canaster of any type under it BUT if I remember correctly I do remember seeing a metal line running on the inside of the frame rail on the passengers side.
I have crawled under to see if there were any of the rubber fuel lines collapsed and there were none. Since it has dual tanks I would assume there should be a canister for it? I replaced the Auxiliary tank with a new plastic one a couple years ago but don't remember seeing anything (but my memory fades with age). I know I would like the lease obvious solution. Meaning if I can get away without having a metal canister hanging off the Bronco I'd rather go that route.

Also Im running a electric fuel pump with a carburetor if it matters

 

[DirtDonk]

A single canister was used even for dual tanks. In the later style like yours probably had, the auxiliary tank vent tube was simply tied into the main tank vent tube with a Y fitting near the crossmember on the driver side between the two tanks. You’ll see the steel line running from that side across the crossmember to the passenger side where it then goes forward. You can follow that steel line and it will probably tell you which style of canister you had based on the direction that the end is bent.

Another clue is that if it did run on the outside of the passenger frame rail and had an anti-rollover valve plumbed into it, you had the later style canister.

An alternate clue is to look through the rear driver side wheel well and look for multiple tubes coming out of a body panel above the auxiliary tank.
You can fold the driver seat forward and look behind the corner pillar of the door and if there is a metal panel covering a plastic tank, then you have the early style.

 

[kat]

A single canister was used even for dual tanks. In the later style like yours probably had, the auxiliary tank vent tube was simply tied into the main tank vent tube with a Y fitting near the crossmember on the driver side between the two tanks. You’ll see the steel line running from that side across the crossmember to the passenger side where it then goes forward. You can follow that steel line and it will probably tell you which style of canister you had based on the direction that the end is bent.

Another clue is that if it did run on the outside of the passenger frame rail and had an anti-rollover valve plumbed into it, you had the later style canister.

An alternate clue is to look through the rear driver side wheel well and look for multiple tubes coming out of a body panel above the auxiliary tank.
You can fold the driver seat forward and look behind the corner pillar of the door and if there is a metal panel covering a plastic tank, then you have the early style.

Ill check it out in tomorrow and hope to have some pictures. Is there a simpler way to vent the tanks without having a charcoal canister? Since it is recommended to run a vent hose from canister to air breather. I have an aftermarket air breather that has no place to connect a hose. I have searched here and found some strange fixes. Also as I said there is 'hissing' when I open the gas cap, do you recommend a safe way to tell if its blowing or sucking?? My first thought was using smoke off a cigarette lol. I may need to start a new thread to get more info on my situation since Im figured out (with your help) that the gas cap wasn't my issue.

 

[DirtDonk]

haha! Yeah, the cigarette trick works every time!

To tell which way it's going? You just have to feel it. But if stuff is coming out it's a good bet it's pressurizing.
And speaking of the gas cap... Some have simply drilled a small vent hole in the cap to release pressure. People have been doing that for more than 40 years. It's not kosher, it doesn't help with fumes, but it gets the venting job done.

Some aftermarket air filter housings have available fittings. Or you can rig up your own.
Some have simply run a host from the vent tube up into the wheel well and looped it or put a filter on it or just run it up and over and down and all around in whatever manner looks clean and gives you a few feet of hose. It will vent the tank, but it won't do anything for gas fumes in the garage or house.

What type of air cleaner do you have?

Paul

 

[kat]

My air filter is just a small aftermarket one...no place for drilling a hole even.
Well after crawling under it and taking pictures I got even more confused. As you can tell by the fuel tank pic, there is only a filler tube and the overflow hose. I looked on line and new stock tanks have 2 small nipples next to the filler tube, and assuming that is for ventilation. All the under vent tubes are cut off and plugged up on both tanks. The lines go there but are not connected. I really dont want to replumb all the lines for a canister if I can just get away with drilling a hole in my gas caps. As you can tell I have billet covers over them so it wouldn't be noticeable. Would the gas smell be bad in a closed up area?? Right now she stays under a open shed. Also in one of the pics I see a clip on the firewall on the passengers side. I searched and seems people put canisters on this?

Only 2 holes in tank on drivers side

End of vent hose passenger side

Front of rear tank

How big of a hole do I need?? Looks like the cap is vented already but I guess not enough

 

[DirtDonk]

A newer Should be vented one way to allow air in to take up space from the gas being used, but are sealed to keep fumes from getting out.
I’m not sure how large of a hole, but I think people have used 1/64 inch as a size. Better look it up though or wait for others who have done it successfully to chime in.

The firewall bracket is indeed the new style support for the firewall mounted plastic tank. Makes it a piece of cake to mount a new one there. is there a little tab with a hole in it the size of a small screw on the top of the firewall just above that bracket?

 

[Rustytruck]

You should be able to suck air in the vent valve on the cap but not blow out on the later model caps with the deeper locking lugs on the cap and filler.. the earlier caps were sealed and vented through the vapor lines. the charcoal canister and the factory air cleaner the earliest models I have no clue on the sctual vent path maybe the filler neck?

 

[DirtDonk]

From 66 to sometime in the 70 model year there were no charcoal canisters and, as far as I remember, no vent tubes on the tanks at all. Just the filler neck and the fill shutoff tube.

If that’s the case then the early caps were vented both ways. What is normally referred to as a “vented“ cap.