What was found
AFTER STARTING RT ENGINE ODOR OF SMOKE NOTED IN COCKPIT AND FWD SECTION OF CABIN, NO VISUAL SMOKE NOTED, ODOR WAS MORE INTENSE WITH BLEED AIR OFF AND RECIRC ON. MAINTENANCE FOUND BURNED ODOR COMING FROM 31 NAV RX. REPLACED NR 1 NAV RX P/N 622-6137-001, S/N ON 18273, S/N OFF 1652 31, NAV RX OPS CHECKS GOOD IAW SF340 MM CH34.