It's called a headlamp service valve (Ecklers part #A2759). By pulling down on the stem allows you to open the headlight buckets and keep them up when the engine is shut off. They are made of plastic and over time,can develope a crack. It is vaccum operated.

Connect a vacuum gauge to the system just after the port from the intake. Measure, it should be 18 - 20 inches. If not, pinch off the vacuum lines suspect for leaking.....the vacuum will come back up and the miss will go away. Cylinders 6 & 8 get leaned out and she'll miss a little bit making it rough idle. A good diagram of the crazy vacuum system is very helpful and it'll make sense as you move along.

You'll go nuts just ripping pieces apart trying to find problems. The visual indications on you gauge will lead you down a path much easier to find the leak. It can be anything......I gave up and replaced most everything because "everything " leaked just a little bit causing a "big" leak and a miss. The biggest leak was the vacuum switches for the wiper door and the two seperate switches for the headlights on my 72. Even the replacements leaked - I sent one back for warranty replacement.....

Bruce

Your welcome Mike - just take your time and it will become apparent where the leak is eventually. I still think I've got a leak under the dash someplace, most of these parts were difficult to get at and I just hoped they were good enough for the time being....I still have the wiper door open each time I start the car after sitting a few days. It closes right up, but it is annoying and it did not do this before I used the repo parts.

Bruce