Charcoal / vapor / evap canister, how it should be set up and other information

[73fleetsideABQ]

Just to note, on the bottom of the purge valve, the large solo outlet indicates "tank" and the other large outlet under the small outlet indicates "CAN". Thus, I wonder if the vapor line should be plugged into this purge valve first not the canister. Vapor line would go to tank inlet on valve, then large outlet to canister (tank input on canister), and small outlet to timed/port vacuum. Then canister purge would go to PCV??? I'm sure I'm over thinking it but I'm just not familiar with how the purge valve actually operates. Thanks for your thoughts.

 

[SirRobyn0]

Howdy. Just for clarification, for the external vacuum purge valve shown below (Amazon ACDelco Professional 214-2294 Vapor Canister Purge Valve), the small outlet is to ported vacuum (carb), the large outlet underneath the small outlet is to PCV/manifold vacuum, and the single outlet on the opposite side is to purge of canister??

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Yes, that is correct, but I'll paraphrase for added clarity.

The two bigger connections that are across from each other. One end connects to the canister, the other to a manifold vacuum source preferably using a two port PCV valve such as Standard Motor Products V227, it does not matter which one goes to the PCV and which one goes to the canister. The smaller port is the "control port" so if you have the factory thermoswitch you'd connect it to that. If not connect it to ported vacuum on the carburetor.

 

[BRetty]

I also want to say thanks for this writeup and discussion.

On my truck, ('81 350 sbc engine) the canister was long gone. The PO had just cut the 1/4"hard tubing vapor line and squished the end shut with pliers. It was loose up front and getting clipped by the fan blades off and on. I had no idea what the line was for just that it was really wrong.

So I ordered a generic 3-port canister from Summit. Gonna hook it up tomorrow I hope, along with other fuel lines overhaul. Two comments:

It's frikkin HUGE! I expected the size of a soup can, this is like a gallon of paint

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Are these really fragile? Last time I saw this kind of packaging, the box was labeled

LIVE HUMAN ORGANS FOR TRANSPLANT

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[SirRobyn0]

@BRetty Glad it was useful to you as well. Yea, gallon size paint is about right! Is your mounting bracket still there? If not I bet you could get away with using a large screw clamp. The main thing is it needs to be mounted straight up and down. I'd say they are not really fragile, they can handle the worst vibrations a truck can give it, but the sides can be cracked if they are impacted hard enough.

 

[Frank66]

Next. If your factory vacuum controls are gone, or you have an aftermarket carburetor or aftermarket carb and intake how do you set up a canister like this. Simple. If there is no bowl vent on the aftermarket carburetor as is the case with my Edelbrock that the PO installed, simply plug that port with a 3/8" vacuum cap on the canister.

Vapor connection remains the same. PCV connection remains the same. And the line to the air cleaner housing is equipped remains the same.

The manifold vacuum source which can literally come off of any vacuum source that has a manifold signal. It is not to sensitive so using a port on the carburetor that is BELOW the throttle plates is just fine.

And then there is the connection marked control. I described how it would have gone to a themostatic vacuum switch from the factory in the first post. If for some reason you need to enliminate the thermostatic switch, such as it's broken and you can't locate a replacement, or you don't want to see it on your intake manifold you can just connect that line to any ported vacuum source. The biggest difference is that the canister will purge anytime the engine is above idle at light throttle, so even when cold. I doubt anyone would have a run ability from connection the control directly to ported, but because the engine is not warmed up and the catalytic converter if equipped is not warmed up there will be a slight increase in emissions during that time.

Next post I will talk about 2 canister systems.

Very Good information ! Thank You

 

[SirRobyn0]

@Frank66 You are welcome, I'm glad you found the information useful.

 

[gmc85k10]

So im going to probably delete most of the emissions off my truck but before i do, what does the charcoal canister do?

 

[75gmck25]

It collects vapor from the gas tanks and periodically vents it into the carburetor. In general, the venting is usually controlled by engine vacuum, but the exact setup ( canister with built in purge valve, separate purge valve, etc.) varies by year.

 

[SirRobyn0]

It collects vapor from the gas tanks and periodically vents it into the carburetor. In general, the venting is usually controlled by engine vacuum, but the exact setup ( canister with built in purge valve, separate purge valve, etc.) varies by year.

Good short explanation, but I'm also going to add that the charcoal canister makes the vapor system a closed system. If you eliminate it, then you have to vent the tank(s) to the atmosphere, which is likely to make your truck smell like gas at times, but more importantly it keeps moisture out fuel tanks. When we get an older vehicle in the shop with rust issues in the fuel tank most of the time we discover that the charcoal canister has been removed or the system is inoperative.

Do what want, remove it or don't, but before you decide to I wanted you to know there are good solid benefits and reasons to keep it.

 

[1STLS1]

This is the best information on this out there in one place. Great job and thank you!!

 

[Ricko1966]

So im going to probably delete most of the emissions off my truck but before i do, what does the charcoal canister do?

Why would you delete most of the emissions? At least some of it is beneficial,and deleting it may cause drivabilty problems,and loss of fuel milage. As for the charcoal cannister it helps keep fuel from evaporating out of the tank,a vented cap/tank your gas evaporates into the air. The good thing is you won't have to burn it all,some will just go away on its own. EGR is non functional by design when you floor it. So no power loss,but it allows you to run more timing,gives you better mpg,and decreases octane demand of the engine.

 

[SirRobyn0]

This is the best information on this out there in one place. Great job and thank you!!

Thank you, that is why I started this thread!.

 

[75gmck25]

I have another question. When you look at the squarebody GM emissions stickers they all (I think) have a large two letter code at the top, like AM, XC, etc. I assume this code can be matched to a year, engine and vehicle combination, but I’ve never seen a table that listed the codes.

Is anyone aware of a book that lists the codes and what vehicle they match. Wouldn’t that be what a formal inspection station would use to check compliance?

 

[mjck5]

been going crazy trying to find this kind of info online, i have an 86 k5 blazer that i swapped out the 305 with a 400, deleted most of the emissions stuff and have a after market edlebrock carb, this thread has help tremendously. thank you

i know this is a very old thread but im hoping this can get answered, i capped off the middle 3/8 connection, is it fine to leave the middle 1/4 tapped into the bottom 3/8 line, this is how it was stock

 

[SirRobyn0]

@mjck5 I'm glad you found this useful and it's why I started it, there is about zip for info out there it seems.

So that was one way the factory set them up was to split the purge line right before the canister to provide the canister with the manifold vacuum signal, and yes that's fine. That why I said there were numerous factory setups and I wouldn't be able to hit the details of all the possible combinations, but that's just fine to leave the split like it was from the factory.

The middle 3/8" line went to the bowl vent on the factory Q-jet. Since your running an Edelbrock, and Edelbrock vents the bowl to the top of the carburetor in the air cleaner housing there is no provision to hook up a bowl vent, so removing that line and plugging off the connector on the canister is the correct way to handle that.

Basically I wrote a lot of detailed words to say what you have and what you have done is all correct and good.

Let me know if you have any other questions. Thanks.