This is strange, when i gun it from a dead stop it accelerates smoothly with very little hesitation, but when i let off the gas, it stalls out unless I ease off the gas slowly. I checked for vacuum leaks, found none. Timing is set at 8 degrees initial advance, 30 degrees total. The carb in question is a holley 4160 600cfm vacuum secondary model. What are the possible causes of this?? Could it be a power valve problem?? Any help would be greatly appreciated, thanx.