850 DP? could be a pump shot problem, jetting problem, or timing problem. Usually that means you are lean and need to go up a few jets or your squirters are too big and you need to drop down. I'd try and set the total timing at 38* @ 2400 rpm and go from there...and disco the vac advance. I ran a 750 DP in a mild 440 to 12.90's (67 coronet) w/ 31 squirters 6.5 PV, 78 front 84 rear jets.