FuelEconomy.gov is a program supported by the U.S. EPA and U.S. Department of Energy. According to their website, "Manufacturers are not required to test [fuel economy for] each individual new vehicle offered for sale … In addition, some vehicles are exempt from these requirements," including motorcycles.
See FuelEconomy.gov's Web page: Which Vehicles are Tested
In addition to federal regulations, be sure to check with your state to determine if there are additional emission requirements.
See: Health and Environmental Agencies of U.S. States and Territories