I enjoy hearing the engine as I ride. The catalyst does a perfectly adequate job muffling the exhaust note, so I carefully modified the tailpipe.
Janus 250 Phoenix
With a 229cc Lifan copy of a Honda engine, the 275lb Janus is capable of scooting around at <65mph speeds easily. I've modified the intake and exhaust, and rejetted the 30mm pumper carb. It runs much smoother now.