You might also check the vacuum source the line comes off. Best bet is to use a source directly off the intake. If you are using a source off the carb base, it may or may not have vacuum at idle. The carb nipple which has vacuum at idle is the one you want, and is referred to as 'ported'.

At some point in this process, someone is going to point out that at wide open throttle (wot) you loose vacuum, and you centrifugal advance is in control, and you can swap springs for controlling the centrifugal curve, but first let's nail down your base setting.