If it is running rich and place it at half choke that would cause it to run richer. The trend that I’ve seen is that in order to meet emissions the small 2 strokes have run so lean that they are short on power. They don’t have any snap when you crack the throttle and the carbs have no idle mixture adjustment to correct this. There is also no main jet adjustment which is what it sounds like is needed in this case. The best way to tell if it is running rich or lean is to pull the plug and read it.
On a side note running the oil mixture richer does not richen up the air/fuel ratio, so run the oil ratio where it is supposed to be for optimum performance.