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

[84-C20]

Which shop do you manage? I might have to drop in sometime. I did order the canister off ebay. It should be here early next week. Given I've only owned the truck for about 2 and a half years, I discovering more "bubba-isms." All of the emissions are deleted.

Good to know you aren't that far away.

I manage Luke's Redmond Automotive. You are absolutely welcome to stop by sometime, but if we happen to be busy when you drop by we might not get much talk time, but I'll turn you loose to look around the shop especially if we have any interesting classic projects going on. Just tell whoever is at the front desk that your a friend of Rob's. Bonus points if you drive your truck and I get to look at it!

Really great, I don't understand how some folks are ok with not evap system, no air pump and no cat. I tell you I'm

 

[vphouger]

I manage Luke's Redmond Automotive. You are absolutely welcome to stop by sometime, but if we happen to be busy when you drop by we might not get much talk time, but I'll turn you loose to look around the shop especially if we have any interesting classic projects going on. Just tell whoever is at the front desk that your a friend of Rob's. Bonus points if you drive your truck and I get to look at it!

Really great, I don't understand how some folks are ok with not evap system, no air pump and no cat. I tell you I'm

I did run the truck with the gas cap off - ran terrible. I received the new canister and am hooking it up. Now where are those instructions you provided?

 

[84-C20]

I did run the truck with the gas cap off - ran terrible. I received the new canister and am hooking it up. Now where are those instructions you provided?

Page 1, let me know if you have questions... I hope that's your problem. But if it ran bad with the caps off then I doubt the canister will fix it, but at 40 years old I'm sure your old canister is not in the best of shape anyhow.

 

[75gmck25]

For Sir RobynO - my ‘75 K25 still has the original two port canister, and with the original Quadrajet there was a dedicated port for the canister vent line.

When I switched to a newer carburetor I first just put a T in the PCV line to the carburetor and connected the canister vent there, but it seemed to run quite lean at cruise (I have a wideband AFR gauge). I now have the vent line disconnected and left it open in the engine compartment. Truck seems to run fine, but I know the vent should connected somewhere that pulls the vapor.

Where should I connect the vent line for a two port canister? Do I need an external purge valve to control it?

Thanks for any input.

 

[vphouger]

Page 1, let me know if you have questions... I hope that's your problem. But if it ran bad with the caps off then I doubt the canister will fix it, but at 40 years old I'm sure your old canister is not in the best of shape anyhow.

I'm thing the same thing. Thanks.

 

[84-C20]

For Sir RobynO - my ‘75 K25 still has the original two port canister, and with the original Quadrajet there was a dedicated port for the canister vent line.

When I switched to a newer carburetor I first just put a T in the PCV line to the carburetor and connected the canister vent there, but it seemed to run quite lean at cruise (I have a wideband AFR gauge). I now have the vent line disconnected and left it open in the engine compartment. Truck seems to run fine, but I know the vent should connected somewhere that pulls the vapor.

Where should I connect the vent line for a two port canister? Do I need an external purge valve to control it?

Thanks for any input.

Do you need an external control valve. It's not absolute requirement, but it really should have one and might solve your problem.

On a 5 or 6 port canister the control valve part is built in. If you run a 2 port without a control valve it will purge anytime the engine is running. An external control valve is going to have one line going to ported vacuum, which will prevent purge at idle and just off idle, until there is good vacuum at the ported port. It'll also cut the purge as you step on the gas sooner than it would on it's own. Most external control valves need to see around 10 inches of vacuum on the ported line before it'll allow purge. So if you are seeing that lean AFR at very light throttle, before ported would be fully open then adding an external control valve would do the trick.

Connecting the purge line to the PCV line is the correct way to do it.

What you really want is this >>>> https://a.co/d/4wtwQQG <<<< connect it into the 3/8" purge line and connect the smaller "control" line to any ported source. Since fuel vapor does not travel though the control line it can be tee'd into any ported source and it does not matter if it shares that ported source with other devices. This is really the correct way to set it up.

Oh, also running around with the purge line disconnected as you currently are is fine for a while, but eventually the canister will load up with fuel vapors, it'll kill the charcoal and get smelly - timeline on that is hard to say.

Hopefully that helps, let me know if you have questions.

 

[75gmck25]

Sounds like a good alternative to try. My engine runs about 19-20" of vacuum at idle (fairly mild cam), so it will definitely have enough vacuum to signal and close the purge line at idle. I don't have a vacuum gauge inside the truck, so I'm not sure what the vacuum is at cruise.

I run my distributor advance off the full vacuum port, so the ported vacuum is capped on the carburetor. It's an easy fix to add the purge valve control, and maybe it will help with the lean cruise AFR.

Thanks again.

 

[fountain4ever]

We build trucks and vehicles here in Arizona. We use a Vapor Trapper but it goes right to atmosphere. With all the EFI and LS swaps going on, a lot of these trucks have had their canister discarded. But lets be honest, the charcoal would no longer be good in them anymore. The only thing we would like to add is the ability to add the purge valve. Currently we just vent them to atmosphere and this works very good to eliminate the smell and address the moisture issue like another poster had mentioned. We like the Vapor Trapper because it is a nice part and it is serviceable so you can change the charcoal once it gets saturated.

 

[00cls1camaross]

Thank you for making this write up. I have been working on an LS swap for a while now and wanted to have the vapors from the fuel tank go into the manifold. So it is as simple as running the 3rd small outlet vent line form the sending unit, to the vapor canister. -> from the vapor canister to the vapor canister purge valve. -> from the purge valve to the manifold?

What type of gas cap do I need for this? A vented or sealed cap?

 

[EvilGenius]

Thank you for making this write up. I have been working on an LS swap for a while now and wanted to have the vapors from the fuel tank go into the manifold. So it is as simple as running the 3rd small outlet vent line form the sending unit, to the vapor canister. -> from the vapor canister to the vapor canister purge valve. -> from the purge valve to the manifold?

What type of gas cap do I need for this? A vented or sealed cap?

This system should have a sealed cap. Vented cap would defeat the purpose I would think.

 

[00cls1camaross]

I did a little more research after I posted and I agree with you. I appreciate the response as well.

 

[supertrucker]

Posts 1, 2, 3, 4 & 6 are my general information posts, they are all geared towards carbureted rigs, the principles are the same for fuel injected rigs, but the controls will be different.

So yesterday I installed a new Charcoal Canister and did a post in another thread and went on a bit. After I got though with the post I realized I should make a new thread. A couple purposes to that. One would be just to get information out there. It seems like when you look up things like how to set up a charcoal canister on a vehicle that does not have to stock carb it just seems like there is hardly any information out there, but it's really quite simple. Also it can be thread where we just ask general evap questions and hopefully someone will know the answer. And like with the wiper and linkage rebuild threads it can be somewhere we can refer folks to in the future.

I'm going to start with the stock setup and this will be for the 5 or 6 port canisters first found on California emissions trucks, but somewhere in the early 80's they found their way into federal emissions trucks as well. If your truck has two canisters do fret I'll get to that in the end.

So the canister I'm talking about is in the below picture:

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You'll notice 5 visible hoses connections. Lets go over what each one of those connections is for.
Starting with the port closest to the bottom of the picture, and on the bottom of the double stack of connections. That connects to a two port PCV valve and is 1/4" line, this is the purge line. So when the canister is commanded to purge, the vapor stored in the charcoal canister is drawn though that line and into the engine where it is burned off as part of the mixture.

Next the line on top of that is labeled control and is 3/16", when vacuum is applied to that connection the canister purges. I'll elaborate on how to set that up for an aftermarket carb, or on a rig that has had all the factory vacuum controls removed, but if you system is intact and functional you'll want to connect that where it came from. Most commonly it'll be a thermostatic vacuum switch on the intake manifold, or something that branches off of it. I'm sorry I can't be more specific on the factory set up for this line but there were a few different ways it was done.

One the middle set of connections on the canister, the one closest to the canister is a 3/8" connection and that is the bowl vent for the carburetor. If your running an aftermarket carburetor it may not have a bowl vent, in that case it is perfectly fine to plug that port and you can see I have done that on mine.

The 3/16" connection above that is manifold vacuum, it can be connected to any manifold vacuum source, either actually on the manifold or on the carburetor it just needs to have vacuum at idle and light throttle.

Next connection up is for the vapor line off the fuel tank. I don't think I need to say anymore but if someone needs me to elaborate let me know.

And then the black knob like looking thing at the top is simply a vent. If your air cleaner housing has a 3/8" connection on the driver side of the housing then you'll want to pop that black knob off. Under that is a 3/8" nipple and you just connect the two together with 3/8" hose.

A couple pictures of the canister installed with general vacuum hose routing.

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So far most of that I posted in the other thread so for those of you that saw that your probably wondering what the point is here, well hang on I'm about to get into that in the next post.

Is that canister still available? If so where did you buy it. Mine is broken 1986 gmc 359 Pn number 17061006BW. Thanks for writing your article. My center top port is cracked.

 

[sukhoi]

Ok now I should talk about 3 connection canisters I suppose. The three connection canister can be setup as a three connection or two connection.

Here is a kind of poor picture of a three line canister, sorry I don't have one handy to snap a pic of.

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Basic function is the same collects vapor off the fuel tank(s) and burns it off. Setup for a three line is simple and it doesn't matter if the truck has the factory carb and intake or aftermarket equipment.

Starting from the tall port closest to the top of the picture that connection is labeled purge, and it is simply connected to any ported vacuum source, in that setup it simply purges though the ported vacuum. It's not really the best way to setup a canister, but it is the simplest. or it can be connected to an outside control unit.

An outside control unit would consist of a line that runs to the PCV and another to a ported source, with the last line on the controller connecting to the purge connection on the canister. Basically a vacuum control unit and a three line canister function the same as the 5 or 6 line canister it just has external controls rather than internal controls. A guy can put a three connection vacuum canister in a 5 o 6 line truck and using a vacuum control unit have the identical function.

Next port the short one in the middle is where the vapor line from the fuel tank(s) connect.

And the last port in the picture it is plugged off that connects to the bowl vent in the carburetor.

Next and last post in the initial informational will be part numbers.

Old post, I know, but hoping to clarify a possible error for future forum trawlers like myself.

@84-C20, I'm fairly certain that the third "port" on what you're calling three port cans is just the fresh air intake, and should NOT be connected to the carb bowl vent.

Early cans (like the original can on my 1973 K10) had three ports on top and a built-in canister control valve (CARB = ported/timed vacuum, PCV = manifold vacuum, usually teed with the PCV valve, and FUEL TANK from the fuel vent line). Fresh air intake was on the bottom of the can, via a round replaceable filter.

Then in later carbureted years, they added more ports for the carb bowl vent etc, as you so nicely detailed in post #1.

Then, EFI came along, and the cans got simpler again, but they moved the fresh air intake onto the top of cans like ACD 215-153 (gm 17113148). This allows for a fresh air supply tube from anywhere else (often the air cleaner, I believe). What you're seeing as this port being "plugged off" is actually a splash shield for applications without this fresh air supply tube.