Holley stumble trouble

Thanks Matt, that’s all very good info.
I do keep a notebook with different settings/tunes and corresponding results, although I should do a better job of keeping it neat. My chicken scratch can be hard to decipher sometimes!
I think you may be on to something regarding the timing curve. Currently I have 2 lightweight springs in there and the timing comes in hard and fast. I do believe that the carb is very close and with a closer look at the timing I think I can get this narrowed down. I may try some different spring combos to try and flatten the curve a hair.