Somebody ruined a good carburetor! The vacuum advance should not get any vacuum at idle, so if you can see any part of the hole from inside the carb throat with the throttle blade at idle the hole is too big, and/or drilled wrong. I'd suggest plugging the hole with a top hat shaped piece of brass so it can't get sucked into the air stream, and finding somebody else to drill a correct sized hole. Machining the brass plug shouldn't be difficult for anyone with a small lathe and a little common sense.
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!