What was found
AFTER RECEIVING THE ENGINE BACK FROM MFG, YELLOW TAGGED, STICKERED IN THE LOG BOOK AIRWORTHY, REINSTALLED ENGINE. GROUND RUN FOR LEAKS BUT WOULD NOT IDLE SMOOTH UNTIL IDLE/MIXTURE WAS SET AT 625 RPM. OK`D TEST FLIGHT AND IT QUIT ON LANDING. THIS AIRCRAFT DID THIS ONCE BEFORE WITH SAME PILOT, MADE SOME ADJUSTMENTS AND SENT IT UP WITH ANOTHER PILOT TELLING HIM TO WATCH FOR RECURRING RICHENED OPERATION. HE WAS ABLE TO COMPLETE TEST HOP SUCCESSFULLY WITH USE OF MIXTURE CONTROL. AFTER CALLING MFG, REMOVED SERVO PER SI.