[Skuzzy]

Your problem area is occurring at the transition RPM from the idle to main circuits. Seems it is either the idle circuit falling off too early, causing a lean gap between the transition, or your emulsion tube may be incorrect.

If you change emulsion tubes and the bad spot is still there, then it might be time to go after the air bleeders, mixture screws, and/or choke size. I would not change jets, right off the bat.

Hope that helps.