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
I'm sort of confused, you DID back the timing up a couple deg and it stopped?? The mech.
advance would be all in by that rpm even stock, so what is the base adv. set at?? Also is the
vac adv. can hex bodied ? If so you can increase the spring tension, reducing the amt. of adv.
per inch of vacuum.