I have bult a sbc bored .030 over size. Stock internals and heads . edelbrock performer intake. It has a comp cam 12-242-2 I am having trouble with vacuum. It is very erratic the needle jumps up and down between 5 and 15 inches of vacuum i have adjusted carb and still does this checked for intake leaks and can't find any. timing is set at 10 degrees BTdc .I have broken in the cam and proceeded to adjust idle speed, carb settings, etc, that is when i noticed the vacuum doing this .Any help would be appreciated.