I have a 502 chevy with a 850 holley vac sec sitting on a dual plane performer intake.All cylinders run rich except #4 and 6 they run on the leaner side.Would a carb spacer help?Thank you Lorne.
I can't see a carb spacer helping your problem. Since 4 and 6 are lean, it is possible there is a common vacuum leak to both cylinders. Maybe an intake gasket?