It means timing is too low without the vac advance.
Typically you will see anywhere from 10*-14* initial w/o vac advance hooked up, ! port plugged on carb !, and 30*-35* full advance @ 3000+rpm again w/o vac advance hooked up. When you do hook the vac advance up you will see somewhere around 48*-52* @3000+rpm.
Hope that helped a lil.
