Some thoughts:
* This isn't an ignition problem.
* Needles control fuel at midrange, so shimming them to help idle won't work.
* Main jets control fuel only at the high end of throttle openings, so won't affect surging at midrage.
* Velocity stacks will probably mess things up, and don't flow better than the stock intake system.
* These carbs are difficult to get truly clean, and if you miss a tiny passage you didn't see, they won't run right.
But @
ducatiman is the one to help here. It's his business to know all about these 250 carburetors.