What was found
REPLACED RT MAGNETO WITH O/H UNIT FROM O/H SHOP, MODEL 4371, SN 15011241. TIMED MAGNETO TO ENGINE PERFORMED GROUND RUN OPS CHECK GOOD ON GROUND, RELEASED AIRPLANE FOR SERVICE. DURING THE FIRST FLIGHT THE ENGINE RAN ROUGH ON CLIMB, PILOT RETURNED TO AIRPORT. REMOVED RT MAGNETO AND FOUND THAT IT WAS NOT INTERNALLY TIMED CORRECTLY FROM O/H SHOP. RE-INTERNALLY TIMED MAGNETO, RETIMED MAGNETO TO ENGINE, PERFORMED GROUND RUN UP OPERATIONS, CHECKED GOOD. RELEASED ACFT TO SERVICE.