My Tech How-To for the Carbon Vapor Canister

[FSK1460]

After playing around with this thing, it seems to run the best with the restrictive vacuum going thru the vapor separator connected up, and leaving off the other line that's T'ed into the pcv line. So the only other line connected to my canister is the fuel tank line.

Thanks Scotty1998 for staring up this thread. I probably wouldn't have took the time to look into all this otherwise. Plugging up this vacuum leak has sure made a big difference with my rig. Hope others have the same luck.

[GWDriver]

So we really SHOULD use a 'vapor separator'. I can live with that............. One question...........Where do I get one. They seem to be nonexistant. Even my '84 GW doesn't have one. This whole series of vapor cannister articles and write ups have been excellent. Thanks alot.

Oh yeah, again, where do I find the separator?

[turtlejoe]

A piece of plastic somehow got lodged up in there. This is what was causing the "whooshing" sound when I took the gas cap off, which also I believe was causing the running out of gas like symtoms when my tank was low, but not empty.

Was the plastic white? Did it have a small diameter hole through the center of it? I have one too, and my presumption is that it's there to meter the rate at which vapor can reach the canister - in all likelihood, it's an orifice. I do believe it was an original "feature" on my '78 - can't speak to what years had or didn't have it.

This is a great thread, and thanks to Scotty1998 and all y'all for adding to our collective wisdom.

[FSK1460]

Was the plastic white? Did it have a small diameter hole through the center of it? I have one too, and my presumption is that it's there to meter the rate at which vapor can reach the canister - in all likelihood, it's an orifice. I do believe it was an original "feature" on my '78 - can't speak to what years had or didn't have it.

This is a great thread, and thanks to Scotty1998 and all y'all for adding to our collective wisdom.

I believe it was a white plastic piece just as you described. It definitely made a difference after I removed it. Its possible the replacement hose I put on was a smaller diameter and the "orifice" restricted it even further.

[Allen78J20]

Scotty did it fix the problem on your waggy?

[FSJK]

So we really SHOULD use a 'vapor separator'. I can live with that............. One question...........Where do I get one. They seem to be nonexistant. Even my '84 GW doesn't have one. This whole series of vapor cannister articles and write ups have been excellent. Thanks alot.

Oh yeah, again, where do I find the separator?

I was at autozone the other day and grabbed a fuel filter that was set up the exact same way as the stock 'vapor separator'. It was just on a wall in a section with 15 or so different fuel filters.

I should have bought a second, and cut it open, and cut my old one open to compare the internals...but I didn't and just swapped the new one in.

[scotty1998]

After I replaced the canister as per the write up, my vacuum became absolutely steady. All of my surging stopped and all inexplicable weird idling stopped.
You can get replacement cans from RockAuto or NAPA and I'm sure many others. Just used the model #'s provided in the writeup.

[danryanm]

Does anybody have a photo of the electric solonoid for the carb vent? One of the two wires on mine is just hanging and I can't fathom where it should go.

[twmattox]

I just want to make sure I fully understand something about these canisters.

The line going to the PCV will not pull vapor until the purge signal (ported vacuum) is activated, correct??

[scotty1998]

Correct. In its passive state, the purge valve is held over the PCV port with spring pressure. You need vacuum to draw it up to allow vacuum from the intake to pull it out of the can.

Here how it should work.

http://i438.photobucket.com/albums/qq102/scotty1998/JeepVaporCanister.jpg

[Lambrewski]

If that diagram is correct - is it fair to say the tank and the carb vent can go on either side?

My 1406 doesn't have a carb vent, so just cap it off? Looks like it should work fine.

Thanks

[twmattox]

Check out the post by GWChris in this thread:

http://www.ifsja.org/forums/vb/showthread.php?t=87476&highlight=canister

There are a number of them from him talking about taking one of these apart and them having 2 purge stages: an idle stage and an open throttle stage...

Just trying to figure this thing out...

[scotty1998]

Since GWChris has taken one apart and I haven't, I can only assume that he has a bead on the true function of these things behind the scenes. I have no problem being corrected on this issue and would also like to understand the science behind this a little better.

It is my understanding that the carb and fuel tank are passive feeds that when the engine is off, atmospheric pressure lets their vapor be absorbed into the carbon in the can. Then, when the rig is run, ported vac signal does nothing more than pull up on the diaphragm to draw those vapors into the PCV system.

If this is truly a 2-stage system and that there is a low level purge at idle. Then the interior of the can must also have a check valve in it or something similar to block off the carb feed when the engine is running. A diagram of the inner workings would be very helpful.

I'm going to PM GW Chris on this one.

[twmattox]

When all else fails... Read the Manual. I had a bit of free time and read the Factory Service Manual for 1982 (not a lot has changed on these)...

"Vapor Canister
This component is used on all vehicles. The canister is filled with granules of activated charcoal. Vapor entering the canister is absorbed by the granules. The canister has a staged dual purge feature. Two inlets are provided, one for fuel tank vapor and one for carburetor bowl vapor. The outlet is connected to an intake manifold vacuum source. The fourth nipple is connected to the carburetor spark port (ported vacuum).

When the engine is operating, fresh air enters through the inlet filter in the bottom of the canister and purges the stored vapor. When the ported vacuum reaches 12 in. Hg (41 kPa), the secondary purge circuit is opened and the canister is purged at a much higher rate."

[twmattox]

So, I had a couple canisters sitting around and decided to do some investigation. It appears that the purge line does have a metered air bleed. In canisters for older vehicles that do not have the vapor separator (the fuel filter looking thing) the initial (small) purge is in charcoal canister. In newer vehicles with the vapor separator, the initial purge is in the vapor separator (the small line itself). Make no doubt about it, these vapor separators are NOT simply fuel filters. The small line is a metered air bleed...your carburetor is jetted for this and if you use a fuel filter instead...you WILL be running lean. Ask me how I know!

So, on newer canisters, if you place a vacuum on the purge signal in the charcoal canister...it should hold vacuum AND the purge line should not hold vacuum until the purge signal receives vacuum. On older canisters, the purge signal should hold vacuum. However, the purge line will pull a small vacuum and when the purge signal receives vacuum it will purge a greater deal.

There is one more thing. The top of the canisters is a grate like plastic mesh. The charcoal is kept in the cansiter by a sponge looking material. That sponge material on all of mine was deteriorating. So much so that if I turned my canister upside down...I could shake the charcoal out of it. I replaced it with fiberglass mesh when I had the canister open. However, I made sure to doubly ensure that I would not accidentally suck a piece of charcoal into my intake or carburetor by placing a fuel filter in the vacuum lines.