Charcoal canister/ported vacuum switch

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,815
113
The vacuum switch is simply a thermal vacuum switch (TVS), a temperature activated port switch to open and allow vacuum from the carb at 170 deg F or above to draw vapors from the canister. It uses a Canister Control Valve (CCV), a ported vacuum valve just behind the TVS. The TVS has a plastic cap glued on top which is holding a spring down to continuously try and keep the valve closed when the thermal portion expands and pushes up on it. Sometimes that cap cracks and pops off, leaving the valve to leak vacuum like a screen door on a submarine.

When it's off, the CCV loses vacuum and opens to vent the carburetor bowl (3/8" hose on the front of the carb top) to the carbon canister through the CCV if you're TVS is still open. When the TVS cools off, the spring closes the TVS valve in effect cutting off venting the carb to the canister.

The charcoal canister absorbs those vapors from the tank and the carb, and they're supposed to sit there until the engine runs to temp again, getting sucked into the engine. There is an upper and lower membrane inside the charcoal canister that keeps the chunkies in place. If the upper breaks, the engine will suck up some granules. You'll find it in the hose to the TVS, from TVS to CCV, inside the CCV, and into the carb vacuum port. You can take all those hoses off and blow them out, but the canister and maybe the CCV is essentially done at this point. You CAN rebuild the canister with new activated charcoal bits from say the fish tank stuff, but it's a process.

You can try this, although I've never done it- take the TVS off, heat up the pellet end in a pan of water until it gets hot. Then blow air through one of the ports (top port preferably to go backwards), and then check to see that it seats when it cools off. If it does, no need to replace it. Although you can usually find them new for <20 bucks. The CCV diaphragm gets old and cracks eventually then leaks. So I'd just replace that if you're going to be fixing it.

A new TVS is GM p/n 22536551, or ACDelco part number 212-122, or Standard Motor Products PVS-42

A new CCV p/n is GM/ACDelco 17085929, or Standard Motor Products CP108

CCVoperation1.jpg

VIN9canisterventvalvea.jpg

In the picture above from an 87 442 307 VIN9, you get this-
The Blue dashed hose is coming from the charcoal canister to the TVS.
The Red dashed hose is going to the CCV (has 16733 stamped on top of it, #4), it also comes out of the bowl vent on top front of the carb (#7)and comes into the large port on the side of the CCV.
The Green dashed hose is coming from the CCV to the baseplate of the carb (#6). This is where the venting goes for the charcoal canister when the engine is running and TVS is open.
The Tan dashed line (#1) is coming from the air cleaner diverter valve "Y" to provide full time vacuum on the CCV to close the carb vent when the engine runs.
The Orange dashed line is your PCV line to the carb.

Hope that sheds a bit of light for you.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
If you get rid of the charcoal canister and close off all the vent tubes you will need to find a new way to vent your gas tank.
Yep, and old school tank venting causes sludge buildup and gas to go bad fast. The charcoal canister system keeps the fuel system much cleaner.
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
Any kind of vent to the open atmosphere will allow outside moisture into the tank. That is what closed eventing through the EVAP system prevents.
 

Screwz

Greasemonkey
May 10, 2021
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Arkansas
Any kind of vent to the open atmosphere will allow outside moisture into the tank. That is what closed eventing through the EVAP system prevents.
He is 100% correct but a few drops of water in your gas isn’t going to hurt anything. the fuel filter can get any dirt that get into the tank.
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
He is 100% correct but a few drops of water in your gas isn’t going to hurt anything. the fuel filter can get any dirt that get into the tank.

But then the fuel filter clogs faster as well as the lines and anying before the filter. The fuel filter is right up in the carb, so there is a lot of stuff to clog before it. Most fuel filters when clogged will bypass dirty fuel. Also only takes a little moisture to start phase separation which no fuel filter will protect. Gas will go bad in an open vented fuel tank in as little as a couple of weeks. In a closed vented gas tank with EVAP the fuel can stay good for over a year. EVAP is good to have, far fewer gas supply issues.
 

Screwz

Greasemonkey
May 10, 2021
117
43
Arkansas
But then the fuel filter clogs faster as well as the lines and anying before the filter. The fuel filter is right up in the carb, so there is a lot of stuff to clog before it. Most fuel filters when clogged will bypass dirty fuel. Also only takes a little moisture to start phase separation which no fuel filter will protect. Gas will go bad in an open vented fuel tank in as little as a couple of weeks. In a closed vented gas tank with EVAP the fuel can stay good for over a year. EVAP is good to have, far fewer gas supply issues.
I agree that a charcoal canister is the better way but your making sound like if you don’t use it your going to have a bunch of problems. And that’s not true. All you need to do is get some fuel line and a roll over valve . Put a few loops in the line that will get some fuel in them to stop airflow. as the tank get pressure in it the air will just vent . You might need to replace your fuel filter a little sooner . I just don’t see it being a big deal.
 

CopperNick

Royal Smart Person
Supporting Member
Feb 20, 2018
2,223
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Canada
Would hold off on sh** canning that canister until you learn whether or not one of lines attached to it goes all the way back to your gas tank as a vapor breather line. Newer generation tank pickups come with three ports, feed, return, and vent. Vent is just that, a port that allows the tank to breathe so gas enters and exits cleanly and sends the vapors down stream to the canister to be recycled back into the carb.


If you off the canister then be prepared to have to replace it with some kind of inline filter or you will be going nuts from the smell of gas fumes being belched by the tank!



Nick
 
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Screwz

Greasemonkey
May 10, 2021
117
43
Arkansas
Would hold off on sh** canning that canister until you learn whether or not one of lines attached to it goes all the way back to your gas tank as a vapor breather line. Newer generation tank pickups come with three ports, feed, return, and vent. Vent is just that, a port that allows the tank to breathe so gas enters and exits cleanly and sends the vapors down stream to the canister to be recycled back into the carb.


If you off the canister then be prepared to have to replace it with some kind of inline filter or you will be going nuts from the smell of gas fumes being belched by the tank!



Nick
That’s way you should put a few loops in the vent line . You will get a small amount for fuel in the loops that will close the line from air movement.
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,303
113
Galaxy far far away
I agree that a charcoal canister is the better way but your making sound like if you don’t use it your going to have a bunch of problems. And that’s not true. All you need to do is get some fuel line and a roll over valve . Put a few loops in the line that will get some fuel in them to stop airflow. as the tank get pressure in it the air will just vent . You might need to replace your fuel filter a little sooner . I just don’t see it being a big deal.
Except there will still be some airflow, especially as the tank develops some vacuum as the engine sucks fuel out while running. If loops worked GM engineers would have used them over a charcoal can. The tank vents out with the engine off, and vents in while the engine runs. Closed venting does reduce fuel system issues by keeping moisture out. Even the fuel in the loops will still phase seperate and eventually contaminate the rest of the fuel and the varnish clogs the loops, blocking venting and starving the engine.

My tractor has open venting and the gas in it routinely phase seperates and eats the needle valve in the carb. Never had this issue in the Regal with intact Evap. Thankfully it only takes 5 minutes to replace the needle valve in the tractor but still annoying.
 
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