Fuel/air mixture ratio??

Ignition timing should be your first stop.

Throw the book numbers out the window if you don't need to pass emissions. I time stock 340's in the 14-18 range at idle. Set it there and see if it helps with your hesitation. DO NOT hammer on it with this changed, you can hurt the engine because total will be too high. Fix mechanical advance to hit your total number.

If you have the T-quad on it, that may be another area issue.