Your low needle is to rich, the engine can't burn all the fuel it's getting so it slowly loads upmaking it go slower and slower until it drowns itself out and dies. Turn the low needle clockwise about 1/8 of a turn at a time, test your transition and idle each time you make a change. Keep going leaner until the engine won't transition well, then go back richer just until it will transition smoothly, reset your idle speed and fly.