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GM charcoal canister variations


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#1 jd lj

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Posted 10 August 2018 - 05:59 PM

Hi guy's,

I'm wondering which GM/Rochester charcoal canister would be more suitable for a simple set up.

It seems that there's two types between the torana,kingswood's and the early commodore's.

One type has the round purge fitting on top and perhaps a hose or two more than the other type which just has three connections, one of which seems to be usually blocked off.

I'm considering the possibility of using one on a LJ Torana. Now I know that people will be thinking that's a stupid idea and why would you want to do that. Well let's face it these old cars can tend to have more enough fumes coming from them no matter how precisely they're tuned, so the more this can be reduced the better.

So I figure that the charcoal canister would have one line from the fuel tank and one to two from the carburettor air box. So from the air box would it use one line that has two way flow to take the fumes out of the air box when the engine isn't running and then to draw them back out of the charcoal canister when the engine is running at a high enough rpm to suck them back out. However I assume that in this situation the fumes would be drawn out at an uncontrolled rate and could richen the air/fuel mixture too much.

Or

The other canister that has the round purge fitting on top would that be one line from the fuel tank, one one way out of the air box and then the last one out of the canister via the purge fitting which then feeds back into the air box. Would this method release the vapours back out at a more controlled rate due to the purge fitting? Are these purge fittings on early canisters just vacuum operated?

I haven't had anything to do with these in the past so connecting the plumbing correctly to these is something I'm unsure about.

You'd be surprised by how much fumes the air box/air filter housing actually holds that without it these fumes are released to the atmosphere and can find their way into the cabin. It's much better to contain them and burn them as part of the air /fuel mixture.

Thanks for any input.

James D

#2 grumpy xu1

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Posted 10 August 2018 - 08:10 PM

It's been years, since i played around with an lx James, but from memory, the fuel cap was vented, with say a 1/8" hole, 1 breather fitting ran from the tank, to the canister through a 5/16" line, the middle line went to the carburetor & the other 1 vented back to the fuel tank. I "think" have you considered some sort of non vented catch can maybe ? Gary.

#3 jd lj

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Posted 10 August 2018 - 09:09 PM

Hi Gary,

I've got a PCV system set up, the rocker cover has a hose to a baffled catch can that then runs to my air box. This seems to work well.

I recently modified the fuel tank breather line which on the std LJ tank is fitted to the front of the tank and I suspect that when the brakes are applied the fuel sloshes into the vent pipe and being such a small diameter on the std tank it must form a kind of hydraulic lock where it doesn't drain back into the tank properly and eventually fills to the point where the vent pipe then drips onto the diff housing. Either that or fuel is drawn out of the vent pipe by a venturi effect by the air flowing past it.

So I welded a fitting onto the top of the filler neck and modified a XU-1 fuel tank breather pipe to attach to that. This is 1/4" instead of the 3/16" std one and shouldn't have any fuel enter it due to its position. It's routed the same as the XU-1's fuel tank breather too. I've also fitted a baffle to the filler neck many years ago.

Whilst under the car last week I thought that a small filter on the end of the breather pipe would be beneficial and then the idea of the charcoal canister was a step further in evolution from that filter idea.

#4 Cook

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Posted 11 August 2018 - 07:45 AM

James, if you don't mind me adding to the questions, does the car model dictate the canister to be used or is it the engine?  Cheers Ron



#5 grumpy xu1

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Posted 11 August 2018 - 07:12 PM

Hi Gary,
I've got a PCV system set up, the rocker cover has a hose to a baffled catch can that then runs to my air box. This seems to work well.
I recently modified the fuel tank breather line which on the std LJ tank is fitted to the front of the tank and I suspect that when the brakes are applied the fuel sloshes into the vent pipe and being such a small diameter on the std tank it must form a kind of hydraulic lock where it doesn't drain back into the tank properly and eventually fills to the point where the vent pipe then drips onto the diff housing. Either that or fuel is drawn out of the vent pipe by a venturi effect by the air flowing past it.
So I welded a fitting onto the top of the filler neck and modified a XU-1 fuel tank breather pipe to attach to that. This is 1/4" instead of the 3/16" std one and shouldn't have any fuel enter it due to its position. It's routed the same as the XU-1's fuel tank breather too. I've also fitted a baffle to the filler neck many years ago.
Whilst under the car last week I thought that a small filter on the end of the breather pipe would be beneficial and then the idea of the charcoal canister was a step further in evolution from that filter idea.



Have you tried adding a loop in the hose up above the tank height mate, was common in drag racing years ago to stop it.

#6 jd lj

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Posted 12 August 2018 - 07:34 AM

There's no need now that I've made my modification to use a XU-1 breather line fitted to the top of the filler neck. I feel that this is a better design than the original std model fuel tank breather line.




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