I just got my rebuilt motor back and I just fired it up and got it running. Tried to adjust the air fuel mixture screws and couldn't get any more than 6 in vacuume. I have 396 .30 over Rect port heads (840's). Motor is 9.3-1 with comp cam xe284 (240,246 @50) (574,578 lift) and 110* lobe sep. This is the first big cam I've ever had and didn't know if I just have my carb set wrong or if this 6 in vacuume is correct. What could cause this vacuume to be so low?