Emission valve in the air box

It's a PCV valve. It allows blowby to escape the crankcase and enter the intake system without having a continuous vacuum leak. If you don't have the valve, and have trouble setting the idle mixture, you might try plugging the two smaller ports and just have the big one into the air cleaner.

 

I believe that there is just a copper disk on top of the hole- the copper cage just keeps it from falling off. The vacuum pulls the disk down and seals it. I turned one out of aluminum that is more like an inverted top hat when I could not find mine.

 

I believe the disc is phenolic.

 

I was totally unaware of this disc as the car I am working on has it missing. If anyone can post more photos or information on how I can replace this missing part it would be most appreciated.

 

I had the remains of a phnolic disc in mine but it was too damaged to function as anything. I have run without it, but the question remains is it worth having?

 

The disk is a "snorkel" device. It allows pressure in the crankcase (oil vapor) to enter the intake manifold, but prevents atmospheric air from bypassing the carbs. Stated differently, when crankcase pressure exceeds plenum pressure, the disk opens, spilling oil vapor into the throttle intakes. When plenum pressure exceeds crankcase pressure (closed butterfly's - trailing throttle or idle), the disk prevents air from entering the crankcase.

If the disk is removed or missing, and the two small fittings to the intake manifold are not plugged, then plenum air will enter below the carbs directly into the intake manifold. This will alter mixture and make tuning the carbs difficult....if not impossible. The engine will run lean.

Jim S.