Need input from big cam users.

1 what is the cranking compression? A purple [email protected] will be about 160 on a used engine,

2 Google vacuum; fast movement starts at a leak, or carb internal-listen to Cracked. Power valves can drive you insane..

3 Make sure mech advance not fluttering around.

If you have a steady rev, and vac gauge bouncing- look at the valves. Engine is seeing a wrong signal to the intake. Hard to put it in words, something else is making vac erractic (at steady revs).