What was found
NR 1 ENGINE HAS AN INTERMITTENT FIRE WARNING LIGHT AND HORN AFTER DEPARTURE FROM KMIA USING REDUCED THRUST FOR TAKEOFF. THROTTLE WAS RETARDED TO HALF-WAY POINT AND THE FIRE WARNING EXTINGUISHED. TESTED THE FIRE WARNING SYSTEM AND FOUND IT TO BE OK. DID NOT SHUT DOWN ENGINE, ONLY LOW THRUST SETTING BACK INTO KMIA, WITH NO FURTHER OCCURRENCE. FOUND AIR LEAK AT FUEL HEAT VALVE GASKET. REMOVED FAULTY GASKET AND REINSTALLED VALVE PER MM 75-09-01. RAN ENGINE AT BLAST FENCE AT TAKEOFF POWER FOR 3 MINUTES, ENGINES RAN NORMAL PER MM 71-00. NO WARNINGS NOTED. AIRCRAFT RETURNED TO SERVICE. (M)