Gumout is safe for both copper fuel lines and neoprene diaphragms when diluted in fuel. If dirt and grease has entered the fuel line use the new Gumout® Regane Auto Parts Cleaner Degreaser aerosol which has a straw that can reach deep into the lines. If that is not available use Gumout® Jet Spray Carburetor Cleaner. Beginning with the first tank of gas add a high quality fuel system additive to clean areas the spray may not have reached.