[dvcobra]

I have a 351w and it has been backfiring when I accelerate and then let off on the gas quickly. If I decelarte or throw it into neutral it doesn't backfire. My total advance @3000 rpm is at 34 degrees. I checked with a vacumn gauge and it is indicating I might have late ignition timing or possible vacumn leak. Vacumn gauge has a low steady reading.
I am trying to learn how to make these adjustments (timing and carb)so I can do it at the track myself, any help would be appreciated.

I have 2 questions;
1)This may be basic but does late ignition timing mean I need to increase to 35 or 36 degrees or drop down to 33?
2)Any recommendations on how to track down a possible exhaust leak?