Slant six misfire

i am trying to rule out if i have a bad vacuum advance pot.
so when rev my slant six up to 3000-3500 rpms with my hand on the carbs throttle lever when its in neutral if begins to misfire. so i unplugged my vacuum advance from the carb and it does not misfire at any rpm range. could that mean i have a bad advance pot.
OR
can it be too much timing if i turn my timing down couple degrees it well not do the misfire with the advance pot is hooked up to the carb.


its a 225 with a carter bbd 2 barrel all plugs cables ecu are new