Just a follow up here as I was having the same problem. Wrenchbender hit the nail right on the head in my case. I had an .052 jet for a 216 carb in my Rochester that is feeding a 235 cu. in. motor. I couldn't find a bigger jet so I mic'ed a few drill bits until I found one that was .058" and drilled my existing jet out reinstalled the carb for the umpteenth time and my off idle lean stumble was gone ! No more leaving the choke out half way to accellerate.
Moral of the story: check that jet size !
