What was found
ON PUSHBACK AFTER ENGINE START WITH BOTH ENGINES RUNNING NOTED UNUSUAL ODOR IN COCKPIT. F/A A AND B NOTED STRONG PROPANE ODOR IN AFT GALLEY. PERFORMED VISUAL OF 1 AND 2 ENGINE BLEED LINES. NO DEFECTS NOTED. INSPECTED RECIRCULATION FILTER AND FOUND TO BE DIRTY WITH A MUSTY ODOR. R & R RECIRCULATION FILTER IAW AMM 21-22-22 PG 401-406. GROUND RAN 1 AND 2 ENG WITH DIFFERENT BLEED CONFIGURATION WITH NO DEFECTS NOTED. OK FOR CONTINUED SERVICE.