Vacuum advance adjustments?

[Cr33p3r]

Does anyone know how to adjust the vacuum advance on distributors? Now I'm not referring to the timing portion but the actual vacuum adjust. I know on Fords the allen wrench is turned CCW, But I'am not sure exactly what this is doing other than tightening up the band spread for how fast or slow the vacuum advances. How would you know if it needs adjusting in the first place?

[Hypoid]

I'll just leave this here.

http://grantorinosport.org/BubbaF250/perf/perf02c.html

[Cr33p3r]

Thanks Mike, I'll have to check into doing this but I don't have a vacuum canister on the bronco so I need to figure out that part as I go along.