TheSamba.com :: View topic - Carbon Canister Refresh

Tue Dec 01, 2009 3:10 pm

A lot of folks here have asked periodically about the evaporative emissions system; the M26, or otherwise known as 'that emissions crap.'

This is unfortunate, because when most people think of 'emissions systems' in early 70s cars, they think of systems that rob power from the engine.

That is NOT what this is.

When your fuel tank gets hot (like sitting in an asphalt parking lot in August) more of the liquid gas becomes gaseous. Without a way to vent the tank, the tank could bulge or spring a leak. But dumping combustible gas on the ground is not only throwing your money away, its a real hazard for anyone nearby.

The M26 system (which has evolved, but is still in use in todays cars) allows the fuel tank to vent flammable gas out of the tank safely, first to a small chamber under the front cowl (where it has a chance to re-condense and run back in to the tank) or if it is simply too hot to out to allow recondensation, give the gasoline fumes someplace safe to go.

That someplace is the carbon canister. Depending on your year and model, it may be under the front hood, or behind the right rear wheel.

The fumes are captured by the activated charcoal in the canister, and held safely until you restart the engine. A port on the fan shroud allows air to be blown in to the canister, forcing the gas fumes out of the charcoal canister, where they travel up another tube to the air cleaner and are pulled in to the engine and burned.

So you don't waste fuel by venting it to the air around your car, your car doesn't stink because its sitting in a haze of its own fuel, and you don't deform your fuel tank because you give the fumes someplace to go.

Of course, there are two assumptions here: one is that all of your evaporative emissions hoses are in place (like the diagram above) and that they 'air tight' so you're not leaking fuel fumes in to your trunk, or worse, in to the cab of the vehicle.

The other assumption is that your carbon canister is up to the task of trapping the fumes. If it is rusted out, plugged up or the carbon is just OLD, it can't do its job. VW recommended replacement of the sealed canister every 48,000 miles. You can imagine how often this maintenance got skipped.

Finding the canister is easy. But its a sealed steel can. Later models were plastic with a removable top. But even those are difficult to come by, and even if they work, they are often the wrong shape to fit the original bracket on your car.

What to do?

Rebuild your canister! Here's the procedure:

1. Remove your canister from its retaining strap, mark the hoses so you put them back in the right places. (This is assuming you're not replacing the hoses at the same time.)

On the end with two ports, measure in from one side 1-1/2". Drill a 1" hole through the end of the canister.

In the ends, there are perforated plates and a mesh screen to keep the carbon in. Try to keep these against the end you just drilled through while you work, so that you don't get any carbon wedged between the screen and the end piece you drilled through.

Using a screwdriver, use it to loosen the carbon pellets that have packed together in the canister.

When the canister is empty, take a stroll down to your local aquarium/pet store and buy half a gallon of activated carbon used in aquarium filters. Use a collander or screen to shake the carbon so that the dust is removed, and then pour the pellets in to your now empty canister with a funnel.

Finally, get a 3/4" galvanized bung from Lowes/Home Depot, etc. 3/4" describes the STARTING end of the bung, which tapers up to 1" at the top. Thread this in to the hole, working carefully so that the threads of the bung grab on to the screen inside rather than pushing the screen in to the canister.

When you have a 1/4" of thread left on the bung, add some Permatex Ultra Black to the threads and complete your insertion of the bung.

You're done! Now reinstall, and you're ready to go for another 48,000 miles.

Your total cost for this maintenance will be about $1.50 for the galvanized bung, and about $12 for the activated charcoal.

Enjoy. If this howto was helpful, or you think they're is something else that could be added, drop me a line.

Tue Dec 01, 2009 3:15 pm

Very nice... i added it to the FAQS Sticky topic.

Thanks

Tue Dec 01, 2009 3:28 pm

All the pet stores here only have carbon powder, not pellets. However I did find pellets at a Hydroponics store.

Nice write up.

jim

Tue Dec 01, 2009 3:35 pm

Genius! I like that explanation, with photographs too. My Beetle had a later plastic canister which was badly broken where the hoses connected to it and I managed to get a metal one like yours to replace it, now I should be able to restore it :D

Tue Dec 01, 2009 4:00 pm

My 71 Super is missing that whole system, canister and all. Where would I find one to try to reinstall it in it's entirety? It sounds like a fairly important feature that the PO removed for whatever reason.

Tue Dec 01, 2009 5:17 pm

My 68 doesn't have any of the set up.

Where is it supposed to be mounted?

Do any of you have a diagram to set it up?

Tue Dec 01, 2009 5:51 pm

Sticky.
Glenn wrote: Very nice... i added it to the FAQS Sticky topic.

Thanks
Oops, too late! :wink:

Tue Dec 01, 2009 5:53 pm

The expansion tank on my '70 is mounted on the right side of the trunk; the activated charcoal cannister is mounted in the right rear wheel well. Shouldn't be too tough for you to hook up again.
Great write up. My '70 has ZERO fume smell (since I replaced the fuel gauge gasket). I attribute that to all the above components being in place. I'm sure I'll use this writeup to change out the charcoal in the Spring.

Tue Dec 01, 2009 5:54 pm

alex77 wrote: My 68 doesn't have any of the set up.

Where is it supposed to be mounted?

Do any of you have a diagram to set it up?

That's because the system didn't exist in 68. Unfortunately, the earlier cars just dump the overpressure fumes to the ground.

M

Tue Dec 01, 2009 6:03 pm

bayville ss wrote: My 71 Super is missing that whole system, canister and all. Where would I find one to try to reinstall it in it's entirety? It sounds like a fairly important feature that the PO removed for whatever reason.

It is an important feature, one that continues on every car produced today. Last week I had the hood of my daily driver Corolla open doing maintenance; guess what bumped my elbow: the carbon canister.

Replacing all of the elements will take a little time, but will be worth it. All of the parts above the tank in the following diagram would need to be put back in place:

Sorry it looks so daunting; it really isn't. The most important thing to glean from this is that many ACVW owners are corner cutters and think you can improve the design by taking things off...usually without knowing what they do.

My father-in-law is one of them. He saw what I was doing with this procedure and before I got halfway in to the explanation, shrugged and said, "I threw mine away. I didn't know what it did, but it didn't change how the engine ran, so why should I care."

I went outside and beat my head on my fender for a few minutes.

M

Tue Dec 01, 2009 6:04 pm

alex77 wrote: Where is it supposed to be mounted?

Do any of you have a diagram to set it up?
Under the right rear fender, mount it with the single hole face up at a ~45 degree angle facing forward. The thin line comes from the front of the car, under the right running board. The upper hole goes to the fan, the lower hole goes to the air cleaner. The two larger hoses are 14mm I believe.

Tue Dec 01, 2009 6:09 pm

webwalker wrote: Later models were plastic with a removable top. But even those are difficult to come by, and even if they work, they are often the wrong shape to fit the original bracket on your car.
An OG plastic canister. If you're really careful you can pry the top off, refill it and put it back together. The tabs might break though...

Tue Dec 01, 2009 6:12 pm

I expect that Interstate VW probably has the canisters by the pound. I have yet to go to a swap meet where there weren't at least two for sale. The one in the pictures was bought for $5. You should be able to source them out of any 70-74 Beetle, plus Ghias, Buses, and even the Porsche 914 uses the same steel canister.

Tue Dec 01, 2009 7:37 pm

I like the idea completely...heck offer the rebuild as a source of income on an exchange basis. $$$ :D

Tue Dec 01, 2009 8:33 pm

That would require that there be enough interest having an 'all stock' emissions system. My experience (as noted above) is that most dubbers don't care. I offered the howto as one part tutorial, and one part manifesto on why keeping the stock system is a good idea.

Tue Dec 01, 2009 9:32 pm

Good idea and I think I will have to make sure in install everything back in my 71 super when I am at the point of getting things accomplished on it. Any advice of where or how I can plumb the hose that normally connects to the air cleaner on my dual Kads? I was thinking about just welding a round tube on the bottom plate and drilling a hole through it so that it can draw vapors in from there. Sound reasonable?

Tue Dec 01, 2009 9:57 pm

I will try to get everything i need to mount it to my 68 just have to find the the canister de evap tank and the gas tank because the one i have is for a 67

Tue Dec 01, 2009 9:58 pm

Yeah, that would probably work.

How tall will you velocity stacks be on the Kads?

M

Tue Dec 01, 2009 11:07 pm

As far as I know this doesn't apply to my 69, but I'm glad to see that someone finally cares enough about getting the stock system to work to show everyone how to do it! Great job :wink:

Wed Dec 02, 2009 6:23 am

The primary kudos should go to Bookwus who has been PM'ing the howto to anyone who would listen for several years now. My procedure is a minor adaptation of his method.

I figured I'd throw this out there in a more 'in your face' manner to try to get Dubbers to *think* before they start tearing things off their car.

M