What Distributor are You using? The Standard Exchange Units have an Advance Can that is adjustable using an Allen Key through the Vacuum fitting on the Can (If you don't have the Type described by Steve.

  

Does your distributor have the large Hex Nut looking fitting where the vacuum line connects? Those units will un-screw off the pot housing and there are shims there  to set the spring preload.

I've got mine at 7 degrees full vacuum can advance, 26 degrees of centrifugal and the initial at 10. That nets an idle advance of 17 and the stock cammed engine likes that just fine. 

 
 Steve Metzger       Tucson, Arizona

Surprisingly i am not finding a part number online for an adjustable vacuum advance fir the dizzy on my built 292. I have too much advance with manifold vacuum at idle. Thoughts? Part numbers? thanks guys