Thought I had everything dialed in but guess not. Took for a drive today running driving good taking fuel right then I slow down and try to take off again and there’s hesitation one. It gets through low rpm hesitation it picks up but you let off and then try to go back in same thing. Thought maybe I was low on fuel but that didn’t make a difference. Not sure if it’s fuel or fire? If it’s sitting idling and you pump the throttle it’s fine. I recently installed a 195 t-stat new accelerator pump diaphragm spark plugs tuned to highest vacuum etc. timing is at 15 initial. Not sure if maybe it’s too lean? Seemed to do fine until up to full operating temp. Any ideas?

Stumbles can be caused by both lean and rich conditions, lean will have white spark plugs, rich will be black
I like my clean and lean
I just remember one of the stock AAR I worked on years ago didn't like cold spark plugs
What heat range did you install this time?

Autolite 65

Paying VERY close attention from a stop, when you start to accelerate normally does it
1. Pick up / respond momentarily and then stumble?
or
2. Stumble and then pick up a go ?

#2

new problem or been there awhile?
Normally a stumble as soon as the pedal is moved is due to an accelerator pump issue.

Remove the air cleaner,
Block the choke fully,if cold
Bump the accelerator a small amount to release the fast ldle cam.
Look down the center of the carb and as soon as the throttle arm is moved you should see two squirts of fuel, one into each bore. If you don't you have found your flat spot.
Could be several causes but start with the above