1971 Vapor Cannister valve

[Craig H.]

Started to rebuild the vapor canister I picked up a while ago.

First I removed the filter



Then I removed a lot of old foam that was crumbling away inside.

All the charcoal then was able to be taken out and I was left with some more old foam rings inside.

I thought the best thing to do would be to test the operation of the valve.

Dissembled the valve and cleaned all the parts.





After some lubricant on the diaphragm it went back together.





Applied vacuum to the PCV tube and it held vacuum fine.

Then applied vacuum to the carb tube and it opens valve and allows PCV tube to extract contents of the canister.

Problem is it never closes again unless I take it apart and put back together again.

Not sure if I have done something wrong or I am applying too much vacuum and distorting the rubber diaphragm

Any ideas please

[Alan S.]

Re: 1971 Vapor Cannister valve

Hi Craig,
I'm afraid I can't offer any first hand advice.
Have you looked at the information in the 71 CHASSIS SERVICE MANUAL? Section 8-13.There's not any trouble shooting info., but there is a diagram, (cross-section), of the purge valve that may give you a hint.
Also, I noticed the small 3 digit stamp on your canister's top cover. I can't quite make it out. I'm thinking date? If I may ask, what are those digits and when was your car built? My 71, built in mid-January 71, has a stamp of 363. (Notice 2 fonts for the 3s) Many of the parts on my car are dated VERY late in December of 1970; for instance the cylinder case was cast on New Year's Eve.
Sorry I can't help.
Regards,
Alan

[Craig H.]

Re: 1971 Vapor Cannister valve

Hi Alan

The numbers are 209 but this canister is one I picked up from a Corvette Parts Trader so its not original to my car (May 1971) just as close as I could find.

I will give the chassis Manual a look as well - thanks

Craig

[Rich C.]

Re: 1971 Vapor Cannister valve

The contents (charcoal) aren't supposed to be serviceable. So is it empty now? I'd keep an eye out for a nos one, they still pop up. I found one @ carlisle for $60 in the GM box a couple years back. If you don't have access to the service manual, I have an emissions service manual that shows cutaway. You did a nice job cleaning it up though! Usually the rubber seal under the valve tears, thats what i found when mine wouldn't hold vacuum.

[Craig H.]

Re: 1971 Vapor Cannister valve

The contents (charcoal) aren't supposed to be serviceable. So is it empty now? I'd keep an eye out for a nos one, they still pop up. I found one @ carlisle for $60 in the GM box a couple years back. If you don't have access to the service manual, I have an emissions service manual that shows cutaway. You did a nice job cleaning it up though! Usually the rubber seal under the valve tears, thats what i found when mine wouldn't hold vacuum.

Hi Rich

Thanks for the offer , I do have a chassis service manual and have had a look there now.

I know they are not meant to be serviceable but its easy enough to put new Charcoal in them and filters etc.

Being in Australia getting NOS is probably not an option. I picked this one up when i was in US in January but decided to service it before I install it. Car is currently running a generic canister.

I have inspected the diaphragm and cant find any tears but i will remove all the rubber grease on it and try again with lower vacuum pressure.

[Terry M.]

Re: 1971 Vapor Cannister valve

Craig,

Just out of my curiosity, where do you get the charcoal to service the unit?

[Craig H.]

Re: 1971 Vapor Cannister valve

Hi Terry

Go to any pet supply place and get fish tank filter charcoal.

Its used in tank filters and is available in different size containers.

Craig

[Terry M.]

Re: 1971 Vapor Cannister valve

Duhh. I guess you can tell I never had a pet fish. Thanks, and good luck with your 1971

[Craig H.]

Re: 1971 Vapor Cannister valve

I now have the vacuum control and diaphragm working fine.

Cleaned it up and checked for rips and all was fine.

Had a good look at the airflow through the canister when vacuum is supplied to the PVC inlet and it seems to need a bit of constriction (caused by the charcoal) to get the PVC vacuum to drag down the diaphragm against the spring and seal it from dragging fumes.



So my test setup has vacuum going to both the PVC and carb inlets.

A tap on the carb line simulates ported vacuum changing from none to full.

When the car is at idle it has little vacuum on a ported line (as its above the carb butterfly's) so the vacuum on the PVC line drags the diaphragm down and shuts itself off - so no collected fuel vapor goes into the carb.

When the car is in throttle with the butterflies open ported vacuum would be higher and it will cause the diaphragm to be pulled upward and then allow the pvc vacuum line to drag fuel fumes into the carb.

Now next to cut a section of the base out and add some foam filters top and bottom and fill with new carbon.

[Terry M.]

Re: 1971 Vapor Cannister valve

Very nice job Craig. You might consider submitting your work to Vinnie for possible inclusion in The Restorer. While these charcoal canisters started in 1970 (NA9 option), and became standard in 1971 -- they continue even into C4 and newer Corvettes. Now days they are computer controlled, but the basic function and operation is unchanged. I would think there are a lot of us who would want to know how to rebuild one.

[Craig H.]

Re: 1971 Vapor Cannister valve

Very nice job Craig. You might consider submitting your work to Vinnie for possible inclusion in The Restorer. While these charcoal canisters started in 1970 (NA9 option), and became standard in 1971 -- they continue even into C4 and newer Corvettes. Now days they are computer controlled, but the basic function and operation is unchanged. I would think there are a lot of us who would want to know how to rebuild one.

Hi Terry

Once I have successfully finished I may consider it.

I like to not just restore things but understand how and why they work as they do.

Spent ages researching and working with an electical expert friend of mine to work out how the TCS/CEC system works on a 71. The original NCRS article was good but did not fully explain for me how the circuit worked or why it worked. Posted it here...

http://forums.corvetteforum.com/c3-t...id-wiring.html

As well as my 71 Journey thread in Australia

http://www.australiancorvettes.com/phpBB/viewtopic.php?t=6326

My build is not NCRS level or quality but I get a lot of inspiration from what you guys do :-)

Regards

Craig

[Craig H.]

Re: 1971 Vapor Cannister valve

To be able to work inside the canister I cut half of the base out with a sharp blade.



You can see what the inside looks like as well.



There was originally a foam insert top and bottom to stop charcoal getting into any of the vacuum lines or falling out the bottom if the filter element was missing.

This is all that was remaining.

[Craig H.]

Re: 1971 Vapor Cannister valve

Some new foam cut to shape.



And fitted to the top of the canister.



Need to get some carbon now.

[Terry L.]

Re: 1971 Vapor Cannister valve

I'm not 100% sure if this is correct but I think the GM Part no. 7026014 is the charcoal filter replacement.

[Craig H.]

Re: 1971 Vapor Cannister valve

Hi Terry

yes I think thats the filter that goes on top of the grill I have cut off and between the bar and edges that holds it in.

Once i get the carbon in and grill back on I will show adding that as well.

Craig