Vacuum advance issue

In my opionon
the initial advance and vaccum can have been set to facilitate two "fixes" in the past, and those two solutions are not compatible with each other.

1) Today :- enough initial timing to mask the fact that the vacuum can is now disconnected.
2) previously, back in history:- the inital timing was set as per the book nominally 5BTDC, and the vacuum can has been adjusted so that it could be plugged into manifold vacuum port to pull in a lot of advance at idle, to mask the fact that the mechancial advance book setting wasn't adequte for the state of tune or fuel grade. you would get very little vaccum advance from then on up the rpm range, but maximum vaccum advance at idle and just off.
Mechanical advance was still set at book setting from 196?...and that setting is no good on todays fuel , you need 10+*
i.e vaccum advance was used for easy starting idle and just off idle operation
rather than its orginal use on ported vacuum for more advance in the just off idle rpm range
and high speed throttle not quite closed cruise.

hence OP now has 2 parts of 2 solutions in place to mask what was probably sluggish performance off idle or a bloody big flat spot.

as suggested by all/many
wind the vaccum can adjuster totally the other way and start again

and suggested by me
take 1/2 the inital mechanical timing out and start again

increase initial mechinical timing until you get no smell of fuel off the tail pipe at idle with a hot engine, at a guess somewhere betwee 8 and 15*
plug vaccum can in to ported (upper carb vacuum pipe) vaccum
reset idle mixture
reset idle speed to something that means it doesn't stall as you move it into drive from neutral 800-1000 rpm
and see how ya go when driving

if the vacuum can is set right lifting your foot off the gas should result in a feeling that the car will go on and on and on...like a cart on rails, little noticeable G force applied to you to indicate an abrupt slow down once you lift off the gas. try adding a little more until you get to this point, expect it to ping under load if you go too far.

there will be other ways to get it right but sometimes starting again works....

cam cr porting headers all play their part and it will become aparent if your igntion set up can not cater for any modifications to the engine you have made.

dave