I am unclear as to the throttle position when you start to lean it. Lean the engine with the throttle fully open. If the engine still does not transition at half throttle, then the low speed needle may need adjusted. If it just quits as you advance the throttle, the low speed is too lean. If it stumbles and lags, then it is too rich. Be careful, little adjustments at a time, no more than a quarter turn at a time.