I found an online PDF of tuning instructions for my 750 Mighty Demon from the manufacturer, not exactly the same as a Holley but similar enough. In those instructions it pointed out that unless the transition-slot opening is set correctly (throttle plate position), the accelerator pump squirts fuel AS SOON AS the throttle is touched, AND the idle mixture is sufficiently rich, it WILL produce an off-idle bog or flat-spot. Tried it myself, leaned out the idle mixture not even that much (it still idled smooth) and all of a sudden it was hiccuping every time I touched the gas off idle. I gradually richened it back up and miraculously the stumble was completely gone and throttle response was instantaneous.
