Tank Vent

Hi, I picked up a Fuel tank vent vapor can from a CJ7 but have no idea how to plumb it. It was located in the rear driver's side fender and attached to a roll-over valve(which was junk) Any help?? Thanks

 

check out this link... http://oljeep.com/gw/74_76_supplements/GROUP_04.PDF page 14

basically the bottom two go to the tank, the upper plumbs to the charcoal canister.

 

Thanks for the link, but it doesn't show a roll-over valve. Should I have one on both lines from the tank?

 

Your picture shows a liquid check valve.

Emissions changes every year. What's the year? You should put that in your sig or in every message. Hard to help if we don't know what year.

Figure 4-5 - http://oljeep.com/gw/74_tsm/4-FuelCarburetion.pdf

Engine side - http://oljeep.com/gw/74_tsm/4A-EmissionControl.pdf - 4A-16 and 17.

 

Not sure what year it came from, but there was a roll-over valve on it.

 

I think Tim is asking for the year of your Jeep.

 

My Jeep is a 74 w/304. It has none of the emissions/ vapor recovery stuff currently. I was hoping to use this canister as a tank vent valve. Not sure if that is possible.
Ok, someone help me with the actual purpose of this part in the original set-up. Two lines from the tank and one to the charcoal can. Why not just one line from the tank to the charcoal canister with a liquid check valve??? I've opened this part and disassembled the inner parts, and I just don't get it!!! Why 2 lines from the tank??????Thanks

 

When I opened mine up (liquid check valve) it seemed to me that its function was to let the vapors through until you got enough off camber to force liquid gas up the vent which would saturate the charcoal canister. The check valve prevents the liquid from passing by that float inside rising and blocking the outlet. When you get back level, the liquid will drain back through the other line.

At least that's what it looked like to me.

 

post up a pic of the top of the charcoal canister from the cj7 so we can see the fittings and what's written next to them.
My 74 with the 6cyl. just had two outlets. later models have more but you just have to hook them up right and they still will function.

 

I don't think there's anything mysterious about the two lines. The earlier tank had four lines, and an expansion tank. The expansion tank is gone. I suspect they included the expansion space in the tank at the front and back, and needed a line from each. You could cut the tank open and find out.

The TSM describes function of these systems. If you read that, you should understand more about what's happening here. The part is just what the name describes - it keeps liquid out of the vapor recovery system.

Show us the canister. The correct canister for your vehicle will not work unless you use the factory air cleaner.

 

I used a canister with 2 ports from an 80's mustang.

 

Hey ole blue, two ports? One from the tank, and one to where? Thanks

 

One from the check valve goes to the "In". The "Out" goes to the stock air filter housing. There is a nipple it connects to in the bottom of the air inlet.

 

Do you know the year of the mustang?. I have an edelbrock air filter housing with knock-outs for such things. Should work fine if I can find the can.

 

The canister with two nipples almost certainly won't work with an aftermarket open-element air cleaner. You need the original air cleaner with the long narrow snout and the tap at the narrowest part of the snout.

Are you still using the K&N filter? The open element K&N minimizes the vacuum above the carburetor to enhance performance. You won't have enough vacuum above the carburetor to purge the canister of gasoline. The canister will get saturated and stop capturing vapors. It could even drip liquid gasoline.

Get a canister from an XJ and hook it up to the PCV line and ported vacuum. Look at a vacuum diagram for an '80s Jeep. Here's a thread that might help you. http://www.ifsja.org/forums/vb/showthread.php?t=106051

 

86-93 with a 5.0 like this one on eBay
http://bit.ly/13QwyLj

If you get a used one, beware because the charcoal may be already at its saturation point. The new ones don't come with the caps, so they must be separate items.

If you don't have a factory air cleaner, I'd stick with Tim's advice

 

Ok tim, the xj idea sounds good. What actually lets air into the fuel tank to avoid a vacuum situation?

 

The vent is open all the time, passing through the charcoal bed.

 

Ok, so thats what the largest port on the canister is for. Nothing is plumbed to it, correct?

 

Which canister? On the original canister, the can is open on the bottom, and there's a fiberglass fliter that coers the opening.

On the replacement canisters shown in the thread I linked, there normally is a black plastic cap over the vent.

So there's actually no open port in either case.