You should be getting a lot more RPM than that on a 26-10 NX. I think you are too rich on the high end. Some of the midrange problem will go away when you lean it out.

You can also put a deflector plate on the front of the carb. A 1/32 thick aluminum plate just larger than the diaphram cover spaced slightly out from the cover should do it. This makes a dead air space that keeps incoming airflow from affecting the diaphram.