David,
A slight hesitation is usually an indication the carb is going through a lean condition, just as you come off idle and start to pull away from a stop.
Putting a vacuum gauge on a port fitting on the intake (not the carb base) while the engine is at idle should produce a steady reading, with a stock SBF in the area of 22" of mercury vacuum. Anything done to the engine as far as camshaft improvements over stock will lower the inches of mercury vacuum.
When the vac gauge is hooked up, blip the throttle, and make sure to read the vac gauge and remember the reading. A stock SBF with a Holley(and since the model number was not listed in your initial post) will usually read somewhere around 7" of mercury vacuum when the throttle is opened. In my example, the power valve would be an 8.0 or 8.5......meaning the power valve is opening before the engine gets to the lowest vacuum point, to create a rich condition, to overcome the lean condition when the throttle is opened. The rich condition can be addressed by lighter springs in the diaphram or different calibrated power valves. It may take a few trys to dial it in.
On thing you want to watch out for is the possibility of a over rich condition at idle, and getting progessively worse when you start to pull away from a stop. It will seam like a hesitation, but the black smoke behind you as you boot it will let you know a rich condition right away. In this case, if you are running a big cam with alot of overlap, your engine may not be producing alot of mercury vacuum. So at idle, as an example, your gauge may only register 7" of vacuum. And if your carb is running an 8.0 or 8.5 power valve, the power valve is open all the time. (Vacuum secondaries).
I myself, had to go through this learning process with my 289 Cobra. I had a LeMans grind cam, dual Holley 465's, and had a hell of a time from a drivability standpoint, and it would not idle. My mercury vacuum at idle was 6.5" and I ended up putting 2.5 power valves in the carbs. After that point, it idled somewhat OK, and no more problems comming off the line.
Good luck, hope this is some help......
Gary Kadrmas
