[jhv48]

I believe you have a Holley Street AVenger carb. Thus, vacuum secondaries, and electric choke.

My Roush came with the same carb, and after futzing with it for a year, I called ProSystems and had them make a double pumper for me. All hesitation and stumbling problems disappeared immediately, and throttle response was vastly improved.

Just keep that in mind, these light cars do not like vacuum secondary carbs very much. And, you are right, it is a momentary lean condition that is causing the stumble. There are only a couple of adjustments you can make to the secondaries, raising the float level, opening sooner and faster or trying a larger secondary jet. You can try a weaker spring, larger main jet or more agressive secondary cam. But, ultimately, you will probably end up selling it and adding a mechanical secondary carb. Not sure why Roush supplies these carbs, but they all seem to have driveability problems right out of the box.

Have fun.