Joined: Nov 2016
I agree with all of the above points, but I understand the difference between a stumble and a general lack of power. I think I'd double check the timing first, and then test the carb with different accelerator pump settings, as you suggested.
Snapping the throttle plates wide causes the timing to fall flat on its face, as vacuum advance goes away. I'm not sure if you have the Load-O-Matic dizzy or the standard version, but either way, if your timing is too conservative, when you go to full throttle and you don't have enough base timing, your car will hesitate.
I smile a lot. It makes people wonder what I'm up to...