As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSTALLED FACTORY O/H ENGINE WITH AN O/H CARBURETOR ON 8-9-2010. AFTER ONLY 4 HOURS OF FLIGHT TIME, INSTRUCTORS NOTIFIED ME THAT THE ENGINE HAD A VERY NOTICEABLE STUMBLE, POWER LOSS WHEN POWER IS REDUCED FROM FULL THROTTLE BACK TO CRUISE RPM. ALSO BECAME HARD TO ACHEIVE PROPER LEANING AT ANY RPM. CARBURETOR WAS REPLACED BY MFG WITH ANOTHER O/H UNIT.