[68gt500]

What you are describing is a fairly typical lean spot at the point where the mains are not just picking up yet.

You need to extend the working range of the Idle/transfer circuits.

I cured it on my car by drilling the 3rd progression hole.

This is a fairly typical modification done on the IDAs for better street manners.

Using the infos I found in the internet I went ahead an drilled the additional 1mm hole. Pretty straigt forward and the effect has been great. No more stumble.