Vapor Canister

[Odoyle]

I'm in the process of restoring my 83' PF Spider and am noticing a slight smell of gas coming from the vapor canister. Car hasn't been run in the past 2 weeks but today I noticed the vapor canister doesn't even have a cap. Come to think of it, I don't think the car had a cap when I got it so my question is: is this a problem and if so where would i source a vapor cap. Also would it be in my best interest to replace the charcoal in the box?

[bradartigue]

If you don't have the cap then you are letting too much air into the box - it actually screws up the idle on the fuel injection system. Might be hard to find a cap without a canister, but you can use an Alfa canister:

http://www.ebay.com/itm/Alfa-Romeo-Spid ... 88&vxp=mtr

I once took a rubber stopper and drilled a hole through it, then inserted a brass tube of about 2mm in diameter. Worked like a champ. The tube kept the hole open. If you close it off completely you might suck in your gas tank. You could probably do the same thing with a fat O-ring stuck in that hole and the tube in the middle. Fat O-ring size is unknown to the author.

[Odoyle]

Interesting... that could explain why the car is idling high. I'll try and come up with a cap solution and post pictures but could you elaborate on what you explained here,

If you don't have the cap then you are letting too much air into the box - it actually screws up the idle on the fuel injection system. Might be hard to find a cap without a canister, but you can use an Alfa canister:

I once took a rubber stopper and drilled a hole through it, then inserted a brass tube of about 2mm in diameter. Worked like a champ. The tube kept the hole open. If you close it off completely you might suck in your gas tank. You could probably do the same thing with a fat O-ring stuck in that hole and the tube in the middle. Fat O-ring size is unknown to the author.

[RRoller123]

I tried an experiment where I pulled the cap and held my thumb over the canister hole while the engine was idling. It slowed down until finally it would have stalled if I hadn't removed my thumb and let make-up air into the system. I believe that this is the only source of make up air for the gas tank.

[bradartigue]

Interesting... that could explain why the car is idling high. I'll try and come up with a cap solution and post pictures but could you elaborate on what you explained here

Elaboration -

The fuel injection system is sealed - conceptually air enters through a single, metered device (the AFM). Since there are things that must be done (idle when cold, filter gas fumes), there are other devices that the system is designed to take air in from - some work all the time, some work part time. The vapor canister operates full time, a draw of air from the canister to the fuel injection plenum is allowed for in the system design. It is, for lack of any better phrase, an air leak that the ECU is programmed for.

The cap on the canister controls the amount of air entering the canister. It is a lousy design, frankly, since the cap is removable and breaks off easily. I am not sure how much air it lets in - but it is enough to bring the idle speed up considerably when removed and down considerably when plugged.

Your best solution is to find a cap. Next best is to fabricate one as I described, leaving the hole open enough to breathe, about 2mm - 3mm. I can think of all manner of ways to do this - fat o-ring, rubber stopper, big hose/little hose. Once installed you'll need to reset your idle.

[4uall]

well this post has certainly peaked my curiosity From the day I bought Fiona I have never had a cap on my vapor canister and using your info (Brad) I had set my idle etc. I have never had any starting or running issues (that i am aware of ). If I read all the above it would appear that I am extremely fortunate to have no issues or Fiona is alive and wants to live

old pic (no cap)

[bradartigue]

Simply put without the cap you are compensating by having the idle speed screw nearly closed. This isn't necessarily a bad thing, you are just getting the air the thing needs to idle from the canister and not the idle speed bypass chamber.

[4uall]

And this is why I love you.

thanks Brad, ordering canister now

[KevAndAndi]

And this is why I love you.

thanks Brad, ordering canister now

Curious: Why order a canister when you can fashion a cap? (I can understand the impetus to have a completely correct-looking engine bay, if that's the answer.)

[RRoller123]

The cap is held in by two spring arms, and the exposed area is not so easy to calculate. I think another, possibly bigger problem is that the small screen behind/underneath the cap can get clogged with dust and crap and not let enough air in, causing all sorts of mysterious issues.

[4uall]

I had little to no fabricating skills etc I am however, great at following instructions

[KevAndAndi]

The cap is held in by two spring arms, and the exposed area is not so easy to calculate. I think another, possibly bigger problem is that the small screen behind/underneath the cap can get clogged with dust and crap and not let enough air in, causing all sorts of mysterious issues.

Hmm. I'm going to have to check my cap, because my recollection is that there were no spring arms - that it came right off with no resistance whatsoever, in other words, it was just sitting there. It's a miracle it didn't come off while driving! I don't recall the geometry, but I wonder if I could drill holes and hold it in place with tiny cotter pins or even bent pieces taken from a paper clip?

I'm sure the charcoal and foam need to be replaced, too.

[RRoller123]

clips were likely broken off? or design changed?

[KevAndAndi]

clips were likely broken off? or design changed?

Perhaps. It's low on my to-do list, but I would like to rebuild the vapor canister at some point. I saw a thread on this topic that came tantalizingly close to a conclusion but stopped short.

Seems that cutting the bottom off the canister would be fairly easy. As I understand it, it should be attacked from the bottom because the canister septum goes all the way to the top, but it stops short of the bottom. (Someone, correct me if I'm wrong. Not that I need to ask.) Therefore, you wouldn't be cutting the septum.

Then, working from the bottom end, remove the bottom mesh, bottom foam, charcoal, top foam, and top mesh. The mesh could be reused. As far as the foam is concerned, well, I personally hate foam rubber because of its rapid deterioration rate. Ever had a pair of headphones with foam earpieces that lived in a drawer for a few years, and when you pulled them out, the foam just crumbled?

I wonder if something like this would be better for the "foam" layer of the vapor canister parfait:

http://www.amazon.com/Acurel-LLC-Pollut ... rel+carbon

It's a carbon-infused media pad for aquariums. It's cut-to-fit. It's thick and rigid. What's not to love? If it has basically the same properties the foam has (permeable to vapor, impermeable to carbon powder), plus it's actually infused with carbon, that should be a double win.

Glue the bottom back onto the canister, reinstall it, and you're done.

Since it's only six bucks, I'm ordering a pad to see if it appears suitable for the job.

[KevAndAndi]

I received the carbon-infused media pad ("black pad") today. To my mind, it seems an ideal replacement for inferior foam rubber in our vapor canisters. Actually, there is a version of the pad that is not infused with carbon ("white pad"), and that may be preferable as a foam rubber alternative for those who are rebuilding their vapor canisters with powdered carbon. The reason for using a white pad as the layers next to the screen layers (i.e., where the foam layers currently are) is that the black pad does release a few carbon granules when it is shaken, and it is not certain that these granules would be held back by the screen material.

However, one might want to use the black pad in this way: Rebuild the vapor canister "parfait" top down with screen, white pad, black pad material in multiple 1/2" thick layers, white pad again, and final screen. In other words, forgo the use of powdered carbon altogether, using instead the black, carbon-infused filtering pad. This, I think, would result in a stable vapor canister that would last for years without requiring service. The question is: Would the stacked black pad arrangement be as effective as the original design? This I don't know, but my feeling is that it would be pretty close, and it would probably be much more effective than the unserviced vapor canisters most of us are driving around with. It would also be considerably lighter.