One of the tasks I did when bringing my '81 Spider back to life was to clean out and adjust the AAV. Today I revisited it and re-adjusted, and figured out what I believe to be the true, correct way to adjust the valve. I do not believe the frequently-documented method of "pry the flap further open and retighten the nut" is correct.
Details:
Cleaning the AAV has been well documented. Spray with carb cleaner, let soak, rinse with soapy water, clean water, dry out. If that doesn't free it up, try boiling it and/or freezing it to force the plate to rotate. The plate should rotate with some spring force (you can get a small screwdriver in there to rotate it to check if it's free to move).
Adjusting the AAV has been documented here, on a few Alfa forums, and some BMW forums. The general consensus is that you should put a small screwdriver in the "pizza slice" opening at room temp or frozen temp, then loosen the 7mm nut, move the screwdriver to open the flap further, and then retighten the 7mm nut. This biases the AAV to have a larger opening and close later. However, the mechanics of this didn't really make sense to me - it'd be a pretty terribly designed component if you needed to truly jam a little screwdriver in there and press to an unknown degree against a spring loaded plate. It just didn't sit well with my engineer brain.
So, today, I explored the mechanism a little more and discovered that the adjustment nut and threaded shaft itself actually MOVES after it is loosened! It translates in a roughly radial direction from the AAV's centerline. This DIRECTLY adjusts the air gap (aka "pizza slice") slice in the AAV at any given temperature. I found that the easiest way to adjust this is to loosen the 7mm nut, then use a small screwdriver to pry on the washer below the nut to move the adjustment to your desired position, then retighten the nut while still holding pressure on the screwdriver so your adjustment point stays put while you tighten. You can do this at any temperature.
Please see pics below for a better visual explanation. I also documented the aperture size of my AAV at frozen and room temps (with the adjustment nut biased fully to the most-open setting), and at room temp with the adjustment nut biased to the most-closed setting. As you can see, at room temp (about 55-60deg today), this adjustment nut can change the AAV aperture from a "full pizza slice" to almost completely closed. The aperture never FULLY opens at any temp, at least on my AAV. I suspect that's the case for most.
In my case, I biased it to the most-open setting because I needed a little bump in RPM on cold startups on this engine.
I then tested how long it took to close when 12V is applied to the contacts. My AAV took about 3min to close fully. Started at room temp and with adjustment nut set to most-open-position. This seems like it should be about right.
I hope this info is helpful to others and demystifies some of the black magic about how to adjust this valve!!
