they aren't just supposed to have mufflers by law, they are supposed to have either stock mufflers or EPA/CARB regulation/certified mufflers. Its just a question of Db levels as far as the exhaust system goes. Has to meet or exceed the regulated levels for a stock bike of that year.
That is the real law....but if your system is relatively quiet, they won't care if its certified or not. States have been turning a blind eye to bike exhaust system for ages (its always been illegal)...but recently more states are starting to crack down on it, unfortunately mostly due to all the harley's running around at 2am with open straight pipes. Piss off enough people, and everyone pays.
EPA laws are very severe btw. $10K per offense. They consider an offense per COMPONENT that is altered. Thats aimed at business' though, not citizens.
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