It actually sounds like it may be too rich. With the plane held securely, get the engine to full throttle and adjust the high speed needle until you achieve maximum RPM. The richen it a few clicks so it loses 200-300 RPM. Now bring it to idle and adjust the low speed needle 1/8-1/4 turn at a time until you get a reliable, smooth idle and nice transition to high RPM.

It's a good idea to run it to wide open throttle now and then to clear it out while tuning then check your adjustments.

My guess is that you'll have to lean the needles but not seeing the engine in person, I could be wrong.