BTW Holy, Cliff Ruggles is a pontiac guy, and on the forums I belong to. He is known throughout the country as a quadrajet expert. One of his carbs can run around $600 plus and you'll wait months to get it.
But he also has a book out on how to rebuild and tune quadrajets. In addition, he sells a pretty inexpensive rebuild kit with everything you need to properly rebushing and rebuild those things. Once in a while I've seen the book on ebay, but cant recall the title offhand. I'm sure a quick search will turn it up for you if interested. Sometimes bookhq.com can find you used books at reduced prices too.
Yup, I got his book from the library. He's also active on a Buick forum I sometimes use.
So, seeing this thread reminds me...I acquired a numbers-matching carburetor and took it apart. I can't identify the power piston spring; it lacks a stamped part number or color. It's a lot smaller than I expected, having never had a carburetor apart before. It's not the dual-stage spring that was used on some Quadrajets.
I've been planning to take some photos and post on the Buick forum and hope that Cliff can tell me at what vacuum level my power piston spring begins to engage...I've just been lazy.