Those are the bleeder screws and they are set by Holley when the carbs are built. You should never have to go in there. I don't have to fool with these on my Stock Eliminator '67 Z28 race car either. If someone monkeyed with them, they may have to set and recalibrated. Have you checked everything else out on the carb? Warpage, correct jetting, dirt in the carb, etc.
Jerry