Bad vacuum advance?

[astat1]

I am trying to time my stock 440. I have a ported vacuum source that seems adequate. I think my vacuum advance isn't sensing any vacuum at idle. There is no change in timing or obvious engine rpm change when it is connected. There is no change when a vacuum is directly placed on the advance port on the distributor. I tried to see if adjusting the advance with an allen to both extremes without effect and have it now centered (counted by turning allen nut). Does this sound like a bad vacuum canister? Are they difficult to change? Thanks

[craigandlynda]

with the engine off....remove distributor cap....connect a hose to vacuum advance unit on distributor...apply suction to the hose...watch to see if the plate inside the distributor is being moved as you suck on the hose...if it does not, see if the lever from the vacuum  pod is connected thru the little hole in the plate, it will move without pulling the plate if it is not held in place correctly..it may be that simple...if you suck on the hose and get air, and no plate motion, the diaphragm inside the vacuum pod is ripped...if you suck on the hose, get no air, and still get no visible motion, the vacuum mechanism is shot, probably stuck w rust or other problem...when doen, go suck down a beer.