If there's vacuum on the advance unit at idle, you've done some very, very wrong plumbing from the carburetor. Unless you're able to suck a golf ball through a garden hose and keep it up for quite a while, buy yourself a Mityvac pump and save yourself a bunch of effort. Pump the advance to its full travel, pinch the hose off tight with a pair of smooth-jaw pliers, and see how long it takes for the vacuum to bleed off. Half a minute or more is probably OK- - - - -a few seconds isn't.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!