Attached is a photo of the mystery valve in question. It's part of the distributor vacuum advance line; you can see there where it comes out from the TVS switch in the thermostat housing and into the carb.

Ride is a '79 El Camino 305 V8 (federal emissions package, pic also attached).

It looks like a regular distributor vacuum advance check valve with two extra ports sticking out the side. I'd like to replace it with a new one if I can, though if it's unnecessary I'll just delete the part.

 

It delays the dist from getting vacuum advance til its warm, not sure what the exact name is, good luck finding one.A parts store might have a book you can look through. Me, I'd just hook up to strait vacuum & see how it runs.

 

I believe it is called a thermo vacuum switch

 

Searches for "thermo -" or "thermal vacuum switch" just brings up loads of ported vacuum switches, like the one to the left that it's hooked up to. I'm trying to figure out what the coin-shaped valve is and what it's proper name and/or part number might be. Personally, I figure the entire thing can probably be deleted completely and the vacuum line run straight from the distributor into the carb, but I'm hoping for some input from folks who've tried that before and what their experiences were/are.

 

All right I thought I had the answer for you, Sorry.

 

Variable air valve?

 

ported vacuum vavle

 

Vacuum delay valve

 

Apeiron nailed it. After using that name to search, I found the part is also called a "spark delay valve". It'll be easier to find a replacement searching using that name for it, as "vacuum switch", et al tend to point to ported vacuum switches.

I'm not sure folks were actually seeing it, but I circled the valve in question with a red circle in the pic to point out what I was trying to identify.

For posterity's reference: The spark delay valve is between the distributor and carburetor, with its two "disc" ports connected to a ported vacuum switch. From what I can see, all three ported vacuum switches on this emissions package are basically the same part and work the same, but the spark delay is tuning the distributor's vacuum signal and makes that particular line special. For further reference, car runs just fine with the line tied from the distributor directly into the carburetor, but I would figure the valve is in place for a good reason (likely to help it run smoother at cruising speed, and to retain acceleration, power, etc.). In the engine redress to come, two of the vacuum switches are going to be deleted, and the distributor line moved to the switch on the manifold, allowing me to delete the two plugs in the thermostat housing, too, by replacing it with a type that has no ports for vacuum switches. End result: less chaotic-looking motor.

 

It's to alter the vacuum advance behavior when the engine is cold. When the engine is warm, the TVS opens and bypasses the delay function.