Vacuum advance is strictly there for part throttle economy. It has no effect at full throttle so if changing you mecanical advance made a difference, it was wrong to begin with. It also has no effect at idle, so if it is affecting your idle it is either hooked up incorrectly or your carb has not been set up properly (additional airflow at idle) for the large cam. If power is your main goal, it will make little dfference to you. As for jetting, 2 #'s at a time till you quit going faster then back one.