advance dis.. question
 

iv posted this question before.. it was about the adjustable vaccume advance on my distributor. i was told to advance it untill i hear and knock and then back it off a little but it always seems to jump around and i can never find the best spot. so far the best i found is 3 1/2 rotations out. anyone else have one of there and have any info? also what about if i can make it so i can have a vaccume gadge on the engine and adjust it at the same time. then rev it to 3000 and find best vaccume?? would that work? anyone have one of these and found the best spot for it? thanks for anyones help.