What was found
THE ENGINE QUIT WHILE PERFORMING AN ENGINE GROUND RUN-UP. DEFUELED AIRCRAFT AND OPENED FUEL TANK FOR INSPECTION. THE FUEL FLAP TUB WAS REMOVED FOR INSPECTION AND AN AIR PRESSURE CHECK WAS PERFORMED. FOUND AN AIR LEAK AT THE SCREW CLAMP SECURING THE FUEL HOSE AT THE NON-RETURN VALVE. THE HOSE HAD STRETCHED IN TIME AND LOST ITS SEAL. IT WAS REPLACED AND AIRCRAFT RETURNED TO SERVICE. RECOMMEND A BETTER METHOD OF SECURING HOSE TO NON-RETURN VALVE.