EEC Tank/Charcoal Canister Question

[1970GMC350]

Hello all! My 1970 GMC has an EEC tank in it (it was built in California and sold in Oregon). What kind of vent lines is it supposed to have? I also assume my charcoal canister was removed as I can't find it. Does that have anything to do with venting and, if it does, is it possible to buy a replacement one? I can only find one line running from the gas tank to the fuel pump.

I spent last weekend trying to get my Quadrajet set correctly and also replaced the gas cap with a vented one I picked up from O'Reilly's. I immediately had, what I assume, was fuel pressure problems (bubbles in fuel filter, wouldn't idle correctly, etc.) I was thinking it was carburetor problems, messed with the mixture screws and ended up with a huge mess on my hands.

[Steeveedee]

Vapor canisters are still available. It not being there shouldn't make the engine run badly. There is a steel line in the passenger's side "B" pillar. Vapors through it go from the tank to the canister, which should be located below the battery. If there is currently only one line at the tank, someone has replaced the factory tank. So, you really don't need to buy the canister unless you want to buy another fuel tank. Can you provide a picture of the current setup?

[1970GMC350]

Originally Posted by Steeveedee

Vapor canisters are still available. It not being there shouldn't make the engine run badly. There is a steel line in the passenger's side "B" pillar. Vapors through it go from the tank to the canister, which should be located below the battery. If there is currently only one line at the tank, someone has replaced the factory tank. So, you really don't need to buy the canister unless you want to buy another fuel tank. Can you provide a picture of the current setup?

I didn’t see any lines running up the passenger side B pillar. I attached pictures of the filler neck, the line coming out of the tank underneath the truck and I tried to get a good picture of the tank itself. I did see the spot underneath the battery where the charcoal canister would go.

[1970GMC350]

Here’s a picture of where the canister would go underneath the battery. I put the old gas cap back on but haven’t been able to test it as we have severe thunderstorms coming at us. I’m really hoping this venting issue is part of my problem and I didn’t screw the carb up.

Edit: I just noticed the pictures uploaded upside down. I’m not sure why they did that.

[Steeveedee]

OK, I wasn't clear on the vent line. It's inside the b-pillar, if it is still there. The vent line goes up inside the pillar as a standpipe to keep liquid fuel from reaching the canister. If there is only the one line from the tank, you will need a vented cap, as the vapors have no place to go otherwise.

[1970GMC350]

Originally Posted by Steeveedee

OK, I wasn't clear on the vent line. It's inside the b-pillar, if it is still there. The vent line goes up inside the pillar as a standpipe to keep liquid fuel from reaching the canister. If there is only the one line from the tank, you will need a vented cap, as the vapors have no place to go otherwise.

Thank you for your help! I think the “vented” Stant gas cap I bought isn’t actually venting at all. I just tried sucking air through it for the hell of it and it is basically sealed compared to my old one.

[Steeveedee]

Originally Posted by 1970GMC350

Thank you for your help! I think the “vented” Stant gas cap I bought isn’t actually venting at all. I just tried sucking air through it for the hell of it and it is basically sealed compared to my old one.

Your body can't produce the vacuum necessary to overcome that spring, believe me! Use the old cap. We have threads here about reducing the relief pressure, but just use the cap you have, if it doesn't let gas run down the side of your truck like a locking cap.