ECM units on fuel-injected models need to be recalibrated if used with free-flowing air cleaners and/or modified engines. Muffler shells may discolor if ECM units are not calibrated correctly. These mufflers are designed for use on close-course competition motorcycles only and do not conform to U.S. EPA noise emission standards There is no warranty on exhaust pipes and mufflers with regard to any discoloration. Discoloration (blueing) is caused by tuning characteristics, cam timing, carburetor jetting, overheating, etc. and is not caused by defective manufacturing. See Hardware, Chemicals & Tools for products that will help to prevent or remove blueing. Some products may not be legal for sale or use on pollution controlled vehicles, check your local laws and the manufacturers’ information.