[Jack21]

Carb jetting is as much an art as it is a science. It is a function of carb size, engine size, intake manifold type, and camshaft. Looking at your spec's, I'd say your primary jets are too rich, although a 750 is the correct size carb for a 393 ci engine.

Step one. Look in the Holley book and see what jets Holley uses in this carb as sold. Somewhere between +4, and -4 is what you should be using according to Holley, and it could go as much as -6.

Are you using a dual plane, or single plane intake? Dual planes provide a better vacuum signal, and tend to use leaner settings.

What kind of cam are you using? Hydraulic? Hydraulic roller? What is the duration? Hydraulic rollers pull more vacuum than flat tappet hydraulics. Shorter duration cams (under 220 deg intake)pull more vacuum than longer duration cams (over 230 deg intake). The stronger (higher) the vacuum at the carb, the more fuel is being ingested at a given jet size. Have you checked your idle vacuum with a vacuum gauge? If you're getting 11" - 13" vacuum at idle, the standard jet size as the carb comes out of the box new, to -2 jet sizes is a good starting point. If you're getting 15" - 16" idle vacuum, then -2 to -4 jet sizes is a good place to start.

What do your plugs look like? Black and sooty? Black and wet? Too rich. Grey and clean? About right.

The great thing about a Holley, you can tune it. The bad thing about a Holley (particularly a non-emissions calibrated like a DP), you have to tune it.