i was turning the screw in the advance and i heard a "pop" and now my allen wrench will go all of the way in the advance like there isn't anything in there. Can that screw fall out? I suppose its ruined?

Yep, pretty much. If it's the Crane unit you can screw it clockwise until it stops but when you turn it counter-clockwise to increase tension you have to count the turns. 10 is the limit and around 12-13 it can pop out of the threads and get all crookedy inside.

I just bought a new GM HEI style vac adv. canister on Ebay for $15, are these simple to install?
And, when I turn the screw a few times, I should get a different reading on the hand vacuum pump, right?

I hope these are compatible... my dist. is the one on the right.


http://img.photobucket.com/albums/v243/shawntmartin/9159_1.jpg


http://img.photobucket.com/albums/v243/shawntmartin/HEIDistributorOnPB.jpg

I just bought a new GM HEI style vac adv. canister on Ebay for $15, are these simple to install?
And, when I turn the screw a few times, I should get a different reading on the hand vacuum pump, right?

You can install it without removing the distributor, just a bit of twisting and wrenching, not a big deal.

The vac pot should come with instructions but the screw will dictate when extra vacuum advance comes in. By adjusting the screw, you should see a different vacuum reading on your hand pump when the rod starts pulling in.