retrofit/ add charcoal canister to a 71'

[Analog]

My existing tank doesn't have gas tank air vent lines to the motor. It has a vented gas cap. I want to avoid the smell of gas, avoid the pressure that is building up in the tank and to let the fumes be used in a more environmentally sound way. I want to add a charcoal canister and other needed items for that kind of system. Is that an EVAP or what is the term for that?

Holley in-tank fuel pump with 60psi to a Holley sniper EFI was added. I have a return fuel line from the sniper. Earl's vapor guard lines were used. Because of EFI, no carb bowl venting needed.

I don't want to use an old charcoal part because I want it to work and if rebuilding the one on my 1974 TR6 was any lesson, it is that they don't last forever and some can't be rebuilt.

I would appreciate if anyone has info on what I need. I have two plugged openings on the gas tank plus a plugged vent line on the Holley in-tank pump so I have enough places to start at the tank. I'll need a line going up to the engine bay and into some carbon canister. The canister should have a built on valve that can be actuated by vacuum from the motor once past idle which would open the canister which would then suck fumes into the sniper? With only one line like that, where does the gas tank get new air to prevent pressure in the tank?

Thanks for any help,

[tgreese]

You could call it a fuel vapor recovery system or fuel vapor control system. Some years Jeep called it a FTVEC Fuel Tank Vapor Emissions Control system.

I believe the valve in the canister top always bleeds a little vacuum when the engine is running, and opens wider when the throttle opens. It should be connected to ported vacuum. On a carburetor that port is blocked by the throttle flap at idle, and the vacuum goes away at idle. Above idle it's the same as manifold vacuum. Pretty sure that the GM Rochester system has a solenoid for this function, under computer control.

A '71 tank should have a vapor recovery connection at each corner of the tank. This ensures that the air above the fuel always communicates with the vapor recovery system. There should be some device that blocks liquid fuel from getting into the canister; a valve, expansion tank, something. I know a little about the '72 system, which I believe is the same as what came on a '71 if so equipped. The '72 TSM shows it well. From you description, you expect something more modern. The '72 system requires the factory air cleaner to provide the draw for purging the charcoal bed; no active control like you are describing.

Suggest you look at the parts book on the Tom Collins site for a picture of the original plumbing. I think the '72 TSM will help you more, but the parts book is online and free to read and download. Look at group 4 plate 12.
https://oljeep.com/edge_parts_man.html You can buy the '72 TSM on media (cd, usb) for under $25 at RockAUto.

I put a new XJ canister in my J20, but those are NLA as far as I know. I think you'd be better off with OEM Chevy parts and put the valve under computer control. No idea what Holley provides along those lines.

[Analog]

Tim,
Thanks for the 72 book. Mine is too old and didn't show the vent lines.

There are three vent ports on my tank and it does look like the original 72 book had at least three vent lines leaving the gas tank. Most charcoal canisters that I see don't have that many lines in. I assume I can just connect all three lines prior to going to the engine bay and run one line up to the canister? None of those lines shown in the book seem to be only going to an air source to equal pressure in the tank, right? I guess air is getting back in to the tank through the canister which is hooked up to the air cleaner?
It seems like it would be better to have a valve at the canister to keep fumes contained in that part of the system rather than have fumes go to the air cleaner (while parked) which would have an opening to the engine bay even if it is filtered by charcoal first. My Holley sniper will not control a valve so I'll have to do something with a vacuum I guess.

Thanks,

[tgreese]

NP. Glad to help.

You'll notice that the book shows a vapor separator aka expansion tank that's originally in the fender. This gathers the vent lines together and sends a single line forward to the charcoal canister. A '72 V8 also has a check valve on the firewall. In '73 they replaced the expansion tank and valve with a single larger check valve in the rear fender. You can see that in chapter 4 of the '74 TSM, also at the Tom Collins site.

Yes, a single line goes forward. The more modern canisters have 3 or 4 nipples: purge to engine vacuum (the PCV system typically), purge control to ported vacuum, and one or two vapor lines from the tank and maybe the carburetor float bowl. The bowl vent has a solenoid valve inline and is only open when the ignition is off. As you correctly observed, the tank vent line is open to the atmosphere through the charcoal bed. Thus it will scrub any tank vapors exiting, and admit air as needed. I guess the vapor capacity of the charcoal is enough to avoid saturating the charcoal with vapor. Operation of the engine draws air over the charcoal, and purges the stored vapor to be burned in the engine.

[Mopar_guy]

Here's a couple of other ideas. https://www.classicperformancerestorati ... or-trapper
https://www.perko.com/catalog/fuel_syst ... _canister/