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Charcoal Canister - to use or not to use?

23K views 25 replies 20 participants last post by  Colt44 
#1 ·
Just wondered what everyones thoughts are on using the charcoal canister or not? I am swapping in a SBC and want to keep things simple. I've heard some say they don't bother with it at all and some say I should have it hooked up. I have no emmissions requirements to worry about so was kinda hoping not to use it but would like to hear some input, pros and cons. Thanks to you all.
 
#3 ·
My understanding of the canister is to absorb fuel vapors that the carb emits after the engine is shut down. Keeps the gas smell at a minimum.

Maybe someone else can weigh in here as to the benefits of having the charcoal canister?
 
#9 ·
Maybe someone else can weigh in here as to the benefits of having the charcoal canister?
Maybe someone can weigh in as to the benefits of not having the canister.

Seriously, it's such a basic system to grasp and keeps fumes out of the atmosphere, so I don't understand how not having it makes any sense. The "simple" argument doesn't fly IMO. It takes all of five minutes to understand.:confused:
 
#5 ·
OK, all you Jeep guru's, answer me this:

If millions of Fords, Chevrolet's, Dodges, etc. built during the 60's and 70's ran fine without a gas tank vent line and charcoal canister, what makes AMC so special?
I've got a 360 in my 1983 CJ-7. Figured I'd keep it simple.
No cannister, no vent line and a normal fuel filter. (No return line)
The way I see it, if it worked all those years on every other make of car, it should work just fine
on a Jeep. 2 years since the engine swap and everything runs like a clock.
Am I missing something here?
 
#7 ·
The canister collects fumes from the gas tank and acts as the gas tank vent. It is a passive system in a way that doesn't affect performance. It also feeds a flow to the PCV system when you are at speed which balances it. The PCV system controls engine sludge and blowby. I suppose you could get a '60's PCV valve, but...

It also sends these gas fumes back to the engine to get reburned so it saves gas mileage also. Well, every little bit counts.... ;)

The old style cars used a vented gas cap so the gas tank wouldn't vaporlock when in use and could blow out fumes when sitting. Old cars always stunk like gas when you let them sit in the sun.

AMC used a modern sealed gas tank system. I know for sure when I plug up the $2.00 air filter on the bottom of my canister playing in the mud, a vacuum forms in my gas tank and the engine starves to the point of not running on the highway unless I crack open my gas cap.

I ran with just an open vent when my canister failed and we got bad raw gas fumes in our hair and clothes even.

AMC also got smart and used a return line off the top of the gas filter to blow vapor back to the tank when it gets shut down hot thus preventing vaporlock on a hot shutdown like a lot of old cars did.

I think these are good ideas and should be used.
 
#11 ·
The canister collects fumes from the gas tank and acts as the gas tank vent. It is a passive system in a way that doesn't affect performance... It also sends these gas fumes back to the engine to get reburned so it saves gas mileage also....

I think these are good ideas and should be used.
It is not a question of whether or not it runs better or worse if you do or don't have a canister, there are more benefits to having one than not. Mike nailed it! It acts as a vent, greatly reduces hydrocarbon emissions, stores your ~$3.20/g gas vapors to get burned at cruise and has no effect on performance.

Maybe someone can weigh in as to the benefits of not having the canister.

Seriously, it's such a basic system to grasp and keeps fumes out of the atmosphere, so I don't understand how not having it makes any sense. The "simple" argument doesn't fly IMO. It takes all of five minutes to understand.:confused:
There are no benefits to not running one. You nailed it right on the head.
 
#10 ·
My CJ5 is currently running fine without one. When I bought my CJ5, it was missing the canister and bracket. IMHO, if you already have the components, used them. If you still don't want to use them, I will be happy to them off your hands and intall them on my CJ5.
 
#12 ·
Right now I wish I didn't have one on. I have lost about a gallon of fuel today through it. I parked it this morning after refueling and look down to see a huge puddle of gasoline on the floor. Now I need to do a search and find out why. I thought the vacuum lines were routed correctly.
 
#18 ·
That usually indicates a stuck float needle. this allows gas to overflow the carb float bowl and run down the vent line to the canister and right out the bottom.

The gas tank vent lines should have a liquid check valve on them to prevent gas from filling to get up the line to the canister. My 20 gallon ones are built into the tank, 15 gallon ones are external.
 
#14 ·
Not to hijack this thread but this is my 2nd fillup since the rebuild. It did not happen on the first fillup. This is the warmest day we had though I think. I am reasonably certain the stuff is routed correctly but maybe the lines got pinched or the valves stuck.
 
#20 ·
my 79 doesnt have one anymore either, i sealed it all up and have a vented gas cap.
 
#21 ·
FYI, these purge at two different levels. There is a primary purge (which operates only at idle). A secondary larger purge opens when the purge signal is opened with ported vacuum (so operates at off idle to wide open throttle).

A couple of things most people don't think about with these is that the carburetor was jetted to operate with it. Basically, these function as an air bleed (adding air) to the intake. So, the carburetor is jetted rich to compensate. So, remove the charcoal canister and retain the stock carb...and you will run rich.
 
#24 ·
1979 cj7 258 inline 6

im a brand new jeep owner and im trying to figure out the horrible gas fumes from the exhaust and extremely bad gas mileage on my 1979 258 inline 6. idles and seems as tho it runs good, p.o had vacuum lines a mess. I have a front and rear cto and neither are hooked to anything. can somebody direct me on what to do? I did put new plugs in....
 
#25 ·
im a brand new jeep owner and im trying to figure out the horrible gas fumes from the exhaust and extremely bad gas mileage on my 1979 258 inline 6. idles and seems as tho it runs good, p.o had vacuum lines a mess. I have a front and rear cto and neither are hooked to anything. can somebody direct me on what to do? I did put new plugs in....
Here's what your vacuum layout looked like from the factory.

Hope this helps,

Matt
 

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#26 ·
Having done the 4.0 headswap on my '83, I just went through this. I left the canister unconnected on the first go-round, and although the engine worked fine, I did often have the lingering and not so subtle aroma of raw gasoline billowing around the Jeep whenever it was parked. On hot days after a fillup, as the cold fuel fresh from the underground tank warmed up in my gas tank, I would sometimes even find fuel spots on the ground.
The plumbing is a little simpler for the MPFI setup, so I went back to the junkyard and pulled the cannister and plumbing from the '91 Wrangler donor. After hooking it up, all those fumes go into the intake instead of the atmosphere, and all the gas I pay for gets burned. No more gasoline stench, and no more dripping fuel. Don't have to worry about pressure differential between my gas tank and ambient. MPG went up a tad. I'm not a big environmentalist by any means, but it's nice to know I'm not polluting when I don't have to be.

My advice is, hook it up.
 
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