Sounds like mid-range richness..
If your carburetor's throttle is a slide-type with a tapered needle that moves up and down in a "needle jet" hole, the needle will have positioning notches on it. Perhaps 4 or 5. A clip inside the slide cavity selects which notch is used.
So, the needle position can be raised (enrichening mid-range air:fuel mixture ratio) or lowered (leaning mid-throttle mix).
The particular taper and clip position and length of the needle partly determines the air:fuel mixture ratio delivered around mid-throttle.
The factory probably set the clip on the middle groove. Try moving the clip position one groove up or down and road test the bike.. You should be able to feel and hear a difference.
But first make sure the engine, bike and carb etc. are otherwise in good tune. I'd be specially attentive to the carb since you have minor idle problems.. Both problems could be due to something like a high float level, choke trouble or other rich-running condition. So, try to get that straightened out (check float level, air-filter cleanliness, carb cleanliness, cable adjustments etc.) before adjusting the needle.