Have you made sure there is no vac leaks ? When i put my holley on I had a big hesitation and remembered I left a vac line off , once i put that on I had a small hesitation usually over come with a full throttle pull but always present at light throttle , i found a cracked vac line and all is well now 

I think I fixed most of it!  These Holleys have a small set screw to barely crack open the back barrels at idle.  It's upside down, tiny, and you have to use a right angle screw driver with a very small bit to get to it.  I monkeyed with that a couple of years ago, so I backed it out a quarter turn and most of the hesitation is gone.  I guess I was getting too much air through the back barrels.  I still might try going back to ported vacuum to see what that does.

Just for the edumacation of us carb-challenged folks, what is the power valve?

They are in carburetors.  Mostly Holley.

the power valve  works in combination with vacuum, to richen the fuel supply to the carb under heavy  load, the number stamped on the power valve tells you when it opens, my 750 has a 65 which opens at 6.5 Hg of vaccuum. 5 months ago I suggested that you go back to portd vacuum rather than direct vac, I assume your MSD dist. has a vacuum adv. canister on it, did you try it, and if so what happen, I'am friggen pissed because this afternoon I spent about 45minutes explaining why you don't use direct vac to the canister and when i Clicked on the post button it went to never never land, think about it, if you put 12 degrees of initial into the motor and plug you canister into direct vac. and the canister has lets say 12 crank degs. of total advance built in it you now have 24 degrees of initial at idle, right? wrong! static means it doesn't move, because  the advance canister  varies advance with throttle position and vaccum  at low to mid range your initial is moving around causing either a surge or stumble, I'll say it again, plug it into ported vac. just like factory, holley, edelbrock suggest and forget the BS on how cool, and good they run with direct vac. and let me know.

|UPDATED|9/29/2012 6:07:44 PM (AZT)|/UPDATED|

Serenity now, serenity now.    Thanks for the reply.  For the first time in a month, it's been raining all day here in N. Tejas, plus, it's College Football Saturday.  So I haven't been able to play with the vacuum source yet.  I'll get to it sometime this week...err... month.  Gotta chase down this blower high speed thingy too.