[decooney]

Michael,
In addition to trying jetting changes, do these carbs by chance have the removable discharge nozzles for primary and secondary? Have you tried changes to these along with experimenting with different accelorator pump cams? Maybe try this after exhausting all rejetting attempts.

Also, as orginally equipped I noticed there is a pretty good jump down in original jet sizes / stock rear metering plates between these 4224/660s (Primary 76 jets) you have as compared to the 1850/600 carbs (Primary 66 jets). As a guess... If they are still 76s in the front, I'd be tempted to jump down and try the 66s. The standard 600s run the (F)66,(R)plate 134-9, 6.5 Power Valve from Holley... I'd be curious to know how it works out once tuned a bit more. Good Luck.