I might have an old factory electronic vac distrib to upgrade. What can be tuned with the vacuum advance? I heard about tightening up something in the canister to raise the vacuum required to move the arm. How can you tell which canisters can do this? Is there a way to limit the amount of vac advance and not just the amount of vacuum required? I think I had misfires from too much vac advance in the past which is why I changed to all mechanical.