As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE HAD VERY ROUGH AND RICH IDLE, COULD NOT ADJUST IDLE MIXTURE IAW AD. FUEL SERVO WAS INSTALLED ON A FRESH O/H ENGINE AND FUEL SERVO WAS ALSO FRESH FROM O/H. ENGINE WAS OPERATED AND LEAK CHECKED. AFTER .2 HOURS OF ENGINE OPERATION. FUEL SERVO BECOME ROUGH AND RICH. IDLER MIXTURE COULD NOT BE ADJUSTED.