EPA's Regulations for Smog, Soot, and Other Air Pollution from Non-Electric Motorcycles provides links for all the rules affecting motorcycle emissions.
FuelEconomy.gov's Which Vehicles are Tested says that "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. (FuelEconomy.gov is a program supported by the U.S. EPA and U.S. Department of Energy.)
In addition to federal regulations, be sure to check with your state air and transportation authorities to determine if there are additional emission requirements.
See: Health and Environmental Agencies of U.S. States and Territories