The problem is exactly as I expected
There should be another hole there! The holes are supposed to be equidistant along the tube essentially one for each quadrant of the throttle range. This is actally cause for tuning problems on the OKO carbs (Keihin PWK copy).
The easiest fix is having a hand drill with the itty bitty bits, figure out which one matches the holes as close to exact as possible, and then reaming them all out the next size up and then ride testing the difference. If it still acts flat open the top pair of holes one more bigger and go from there.
The correct way is getting the correct emulsion tube because hand drilling the brass precisely is nearly impossible with that small of a bit.