I'm amazed by the number of flyers who don't set the high speed needle with 1/2 a tank and with the nose of the model straight up. Once the engine is in a fairly clean scream for 1/2 a minute, give the line a quick pinch. The rpms shouldn't drop, they should not go up either, just remain the same. From here you have a solid basis to work on the low end mixture, but the low end adjustments will make you revisit the high speed adjustment as a double check.