I know this is the A Body forum but maybe someone ran into the same issue,Posting for a buddy of mine, 67 Charger with the original factory installed 440 with automatic. Solid lifter cam nothing crazy Holley street dominator intake, 850 Holley carb, stock exhaust manifolds with 3:91 gears. The car runs strong but has developed a secondary stumble with the 850. Tried bigger jetting and gets worse. Put on a Edelbrock 650 AVS-2 great throttle response but still has secondary stumble. Put the 850 back on tried different rods and springs same issue. Put an older 625 Carter on and same issue secondary stumble, tried jetting up the 625 and stumble got worse just like the 850. So obviously not carburation has to be ignition, it does have the Chrysler electronic ignition and we did try a different orange box but no change, timing is 12 degrees initial and 35 total, so where do we look from here.