I found that leaning out the top end significantly improved the mid range burble. I still don't have any overheating issues. A friend tuned his engine by leaning the low needle until the engine sags with throttle application after startup. He says when the engine gets to operating temperature, it is a nearly perfect mixture, and his engine does run very well. I think backing off the low needle by 1/8 turn is too much; it is a pretty sensitive needle.