[Hotfingrs]

From an article in Carcraft....just a thought in the last paragraph

Tuning for Power
An earlier test drive revealed a disproportionate surge of power at low rpm, so Patterson figured the power valve was opening too soon and dumping excess fuel in before the mild-cammed motor needed it. He hooked up a vacuum gauge to full manifold vacuum, gunned the motor a couple of times in neutral, and found a hesitation right around 6-inches of mercury (in Hg). Removing the primary bowl and metering block revealed a 6.5–in Hg power valve, which Patterson promptly swapped for one that opened at a 3.5–in Hg vacuum signal. He noted that correct power-valve sizing should help throttle response at tip-in.

But one thing often leads to another, and installing the new, later-opening power valve meant we'd lost low-speed enrichment and developed an off-idle hesitation. Off came the metering block once again, and the stock 65 jets were swapped for larger 66s. Problem solved.