Hard Starting After Warmed Up.....Arrrg

Bruce. With all do respect, I still am not getting it.
If I set the "initial" timing (with the vacuum blocked off).... say I set it at 12° btdc.
I am reading mechanical degrees...right..??
Now...am I supposed to unblock the vacuum advance tube and place it back on the dizzy ??
If so..I am not for sure how to adjust the limits of the dizzy with the advance hooked up.
I know it can't be that hard to understand....but I am still missing something.