Ok, this seems like the place to answer my question. I unplugged my vaccum advance and set my total timing to 38 at 3000 rpm. This caused initial timing to be 16 degrees. I plugged the vacuum advance back in, on the driver's side port on a Edelbrock 750, and the timing went up to 39 degrees. I have a Mallory Unilite and I believe the vacuum can is adjustable. Does this mean I have 23 degrees of vacuum advance? What should I adjust it to? To check my curve, noting the timing every 500 rpm, should I do it with the vacuum hooked up? This is for a 383 stroker. Wish I knew all the exact specs but I don't. The vacuum at idle is 15.