What was found
(CAN) POOR ACCELERATION AND SLUGGISH PERFORMANCE DURING POWER UP AND DIFFERENT POWER SETTINGS. WHEN APPLYING POWER, ENGINE STUMBLED. INITIALLY SUSPECTED CARB ICING BUT GROUND CHECK RESULTED IN SAME FAILURE TO PRODUCE POWER. PRELIMINARY D/P CHECK SHOWED LOW POWER ON 3 OF 4 CYLINDERS (42-52 PSI) CYLINDERS DISMANTLED AND FOUND EXHAUST VALVES CORRODED AND DETERIORATED REF: SB M90-13. THIS SB SUGGESTS THAT VALVE STEMS, AT TIME OF OVERHAUL, SHOULD REQUIRE 100% REPLACEMENT. THIS IS THE SECOND FIELD EXPERIENCE OF SEVERE CORROSION 400+ HOURS PRIOR TO OVERHAUL.