There are diesel motorcycles, but they are just not as common. HDT supplies them to the Marinees, and here is a write up on them. http://www.autobloggreen.com/2008/02/28/nyt-test-drives-the-marines-diesel-motorcycle/ They remind me of a turboed drag car, they take a second to get going, but then they go. As the report says, they are going ahead on a civilian version. Pretty sweet I think.

As to the illegal muffler thing. Every state/ county/ and most the time city, has its own rules. In SLCounty Utah, a motorcycle can be as loud as it wants. There are no rules for this, they must just pass basic safety. No IM or soundchecks. However if you have a altered muffler on any other type of motorvehicle in SLCity, then you run the risk of being pulled over for 12.28.100 that says if your exhaust "increases, amplfies, or alters the sound of the exhaust" you are in violation. I know speed bumps that can alter the sound of exhaust in the city.