Hi Dave,

I've given up and am sending this engine to YS Performance. I have about 20 flights on it now, and the mid-range is not improving. With the regulator set for optimal throttle response, the engine still still surges badly in the mid-range and at some point usually ends up dying.

I've going to follow the service instructions on YS Performance for returning the unit. I'm also going to include a letter with details about how the engine has been running. Please let me know if there is anything specific I should include in this letter.