What was found
(CAN) FOLLOWING IS SNAG BY PILOT - ENGINE PRODUCED FULL POWER INITIALLY DURING GO AROUND THEN DROPPED TO 2200 RPM THEN BACK TO FULL POWER. WHAT MAINTENANCE FOUND - AFTER THE SECOND OCCURRENCE OF POWER LOSS WE DECIDED TO PERFORM LYCOMING SB 388. (EXHAUST VALVE INSPECTION) BECAUSE WE WERE TOLD THAT THE POWER LOSS HAPPENED WHILE THE ENGINE WAS AT FULL POWER AND NOT DURING THE ACCELERATION. WHEN PERFORMING THE SB WE NOTICED THAT 2 OF THE 4 EXHAUST VALVES WHERE STIFF TO MOVE (#1 AND #2 CYLINDER). ALTHOUGH THE ENGINE PASSED THE CRITERIA LAID OUT IN SB388 DECISION WAS MADE TO REPLACE BOTH THESE CYLINDERS WITH NEW ASSEMBLIES. (TC# 20190718004)