Tuning With An Air/Fuel Gauge

[Captain Obvious]

Yes, I mean RTV.

I'm particular to "Permatex Ultra-Grey" because I've found it to be the firmest (highest durometer) once cured. And in this application where you're trying to seal that flimsy, probably already bent flange using a thin paper gasket, I think the high firmness is especially valuable. It's not really gasoline rated, but in this application, I would still use it. If everything is working as intended, that gasket should be a seal for air, not gas.

I don't think a dry paper gasket is going to get you where you need to be.

[Captain Obvious]

Oh, and in case I wasn't clear... I would use both the silicone AND the paper gasket. I would put RTV on both sides of the paper.

[Captain Obvious]

And I know you don't want to, but this is what I did:     

[chaseincats]

20 minutes ago, Captain Obvious said:

Yes, I mean RTV.

I'm particular to "Permatex Ultra-Grey" because I've found it to be the firmest (highest durometer) once cured. And in this application where you're trying to seal that flimsy, probably already bent flange using a thin paper gasket, I think the high firmness is especially valuable. It's not really gasoline rated, but in this application, I would still use it. If everything is working as intended, that gasket should be a seal for air, not gas.

I don't think a dry paper gasket is going to get you where you need to be.

I wanted to avoid that stuff but if you think that's the only way then I'll go grab some.  You need to wait 24h before starting the car, right?  As a sidenote, could it be that since my gasket doesnt have the other side of the screw holes, the screws are bowing it out, creating the leak?

EDIT: Do you think its possible to fix my carbon canister's leaky vacuum valve?  Are these even serviceable?

Edited March 8, 2021 by chaseincats

[madkaw]

Doing my own wide-band tuning today . Two are better than one !

[Captain Obvious]

10 hours ago, chaseincats said:

I wanted to avoid that stuff but if you think that's the only way then I'll go grab some.  You need to wait 24h before starting the car, right?  As a sidenote, could it be that since my gasket doesnt have the other side of the screw holes, the screws are bowing it out, creating the leak?

EDIT: Do you think its possible to fix my carbon canister's leaky vacuum valve?  Are these even serviceable?

Well that gasket in your pic is (the technical term) "trashed". Even if you weren't going to use any RTV, there's absolutely no way you should reuse that gasket. Not only does it create an uneven mating surface under the bolts (potentially bowing the flange as you mentioned), but it's also permanently compressed.

So in your shoes, if you really don't want to use RTV, you could always try a new gasket first (without RTV) and check it with you A/F meter. If you don't get satisfactory results, you could take it apart again and goop it up.

I'd never been a fan of any sort of gasket compound either, but now I put it on just about everything. I hate seeing big gobs of sealant squeezed out of the gap and I always thought of it as a crutch for people who didn't know how to do things right. Then I started working on lawn and garden carbs where I just couldn't get stuff to seal. So I started putting a little on with a syringe. Just a tiny bit. Now I put a tiny bit on most everything.

And yes... you should give the RTV some cure time before you stress it. Heat helps, so if you put it on your motor while it's still warm from running, it should be good to go the next morning.

[Captain Obvious]

Forgot about the valve on the CARB can... There's not much to it. A diaphragm, a spring, and a metal ring seat for the spring. I looked through my pics for something that might show the guts, but I got nothing. If the diaphragm doesn't have any holes in it and is installed correctly (not folded over), then I don't know what else to do there.

Does the control line (smaller line shared with the distributor advance) hold vacuum?

I do remember someone doing some testing on the valve... @Dave WM   maybe?

[chaseincats]

1 hour ago, Captain Obvious said:

Forgot about the valve on the CARB can... There's not much to it. A diaphragm, a spring, and a metal ring seat for the spring. I looked through my pics for something that might show the guts, but I got nothing. If the diaphragm doesn't have any holes in it and is installed correctly (not folded over), then I don't know what else to do there.

Does the control line (smaller line shared with the distributor advance) hold vacuum?

I do remember someone doing some testing on the valve... @Dave WM   maybe?

It seems neither inlet holds vacuum well.  While the big hose's end won't hold vacuum at all, the smaller hose's valve can be pumped up with my hand-held vacuum gauge but the needle quickly falls after you stop pumping.

I did try running the car last night with the large hose plugged into its intake manifold port (I didn't have the smaller one plugged in for whatever reason) and sprayed the canister's valve with starter fluid to see if the engine idle changed but oddly it didn't.  How can it be leaking vacuum but not raise the engine idle when sprayed?

[Captain Obvious]

9 hours ago, chaseincats said:

It seems neither inlet holds vacuum well.  While the big hose's end won't hold vacuum at all, the smaller hose's valve can be pumped up with my hand-held vacuum gauge but the needle quickly falls after you stop pumping.

I did try running the car last night with the large hose plugged into its intake manifold port (I didn't have the smaller one plugged in for whatever reason) and sprayed the canister's valve with starter fluid to see if the engine idle changed but oddly it didn't.  How can it be leaking vacuum but not raise the engine idle when sprayed?

The small canister hose should hold vacuum at all times. If it doesn't you might want to pop the cap off the carbon canister and have a look around.

The big canister hose will not hold vacuum with the engine off. And that's my little bit of confusion about the system. The FSM talks about the large line as being sealed until the control lines opens it, but in my experience, that is not the case. My theory (that I talked about a little earlier) is that the high vacuum source pulled directly from the intake manifold actually helps pull that large line into a closed position.

As for the other question about not changing the idle... It's probably because that small line (and the distributor advance) is pulled from a ported vacuum source. And at idle, there's no vacuum so nothing gets pulled into the intake tract. In other words, it's not a vacuum leak on that throttle body nipple unless the throttle blade is in a specific position. At idle, there's no vacuum, and at WOT there's no vacuum. The only time there is vacuum there is at a light cruise position.

[Tweeds]

14 hours ago, madkaw said:

Doing my own wide-band tuning today . Two are better than one !

A little off topic here - is it stock for the A/C stuff to be backlit like that? If so, mine never have been. The panel doesn't look stock to my eye - I don't recall it being so shiny, but, then again, maybe I'm not very observant. 

On topic - been following the thread and it's had a lot of interesting information, discussion, and graphs. Great stuff!

[chaseincats]

10 hours ago, Captain Obvious said:

The small canister hose should hold vacuum at all times. If it doesn't you might want to pop the cap off the carbon canister and have a look around.

The big canister hose will not hold vacuum with the engine off. And that's my little bit of confusion about the system. The FSM talks about the large line as being sealed until the control lines opens it, but in my experience, that is not the case. My theory (that I talked about a little earlier) is that the high vacuum source pulled directly from the intake manifold actually helps pull that large line into a closed position.

As for the other question about not changing the idle... It's probably because that small line (and the distributor advance) is pulled from a ported vacuum source. And at idle, there's no vacuum so nothing gets pulled into the intake tract. In other words, it's not a vacuum leak on that throttle body nipple unless the throttle blade is in a specific position. At idle, there's no vacuum, and at WOT there's no vacuum. The only time there is vacuum there is at a light cruise position.

So I went downstairs and popped the cap off the canister and took a couple of pictures of what I found.  The diaphragm doesn't seem to be torn so I flipped the diaphragm over and put the cap back on (pictured is how it was originally) to see if that was the issue then tried my vacuum gauge but it sounds like vacuum is escaping around the cap.  Any ideas?

EDIT: the diaphragm was leaking around the sides and had some small tears.  Since these are nla, can I just plug the big hose directly into the top of the canister?  That would kill the on-demand part from the throttlebody but would that allow the canister to still function?

Edited March 10, 2021 by chaseincats

[Captain Obvious]

What a coincidence... I didn't have any pics of my evap system to refer to aid the discussion, so I popped the cap off mine and took some pics too.  Haha!!

So, I bet I know what's going on with yours... I had mentioned earlier that there's not much to it. A diaphragm, a spring, and a metal ring seat for the spring. Well, you're missing the metal ring seat for the spring. I believe it's purpose is to keep the end of the spring a metal surface to press against to even out the pressure and keep the sharp pointy metal end of the spring from poking through the soft rubber diaphragm.

Well you don't have the seat, and my guess would be that your spring has poked a small hole through the diaphragm. Inspect carefully at the dent where you can see where the spring was pushing:

In any event, it's supposed to look like this:

And I also verified that my small control line does hold vacuum.

About attaching the large line directly onto the post down inside the cap where the spring lives? I think your assessment is correct. It'll be continuously purging at all times. Probably just fine at everything but idle. At idle, you might find it runs it lean again. I don't know if you have enough compliance travel in the mixture screw to compensate, but if you're just looking for an option to try until you can find a new can (or at least diaphragm and spring seat) it's worth a try.

If you find you can compensate with the idle mixture screw, you should be fine.