Check the idle bleeds to make sure they are not closed too far and if that doesn't maybe fatter jets?


Chris

1st step - check for vacuum leaks. Then possibly the following:

Big cams and low idle vacuum can make for an off-idle stumble that's often tough to cure. The problem stems from cranking the primary throttle blades open too far, which uncovers too much of the idle-transfer slot (arrow). When you lightly step on the throttle, the engine stumbles or sneezes because there's no additional fuel available to help accelerate the car, since the transition slot is already in use. The trick is to close the primary throttle blades down to where the transition slot is barely uncovered.

This step will create a too-low idle speed. One way to help that is to crack open the secondary idle stop (located on the bottom of most Holleys on the passenger side) a half-turn or so. If that doesn't help, you might try adding a PCV valve to the carb, which is also a calibrated air leak that will add a little speed. If all those tricks still don't help, you will have to resort to drilling a small hole in each primary throttle blade on the leading edge. Start with a 1/8-inch hole in each primary throttle blade and work up one size at a time. It's a slow process, but that's the best cure for the big-cam off-idle stumble.

Just a thought. Most of the new high perfomance carbs come with the holes already drilled.  Hard to troubleshoot over a forum when the kind of carb is unknown, such as the size and type. But what do I know