It is generally accepted that 2 strokes benefit from having a clean exhaust or ideally, a new exhaust. But 2 strokes have an expansion chamber and the pipe is “tuned” to the motor. So would there be any benefit to having a cleaned or new exhaust system on a 4 stroke?
On a 206 I doubt it. There are some gimmicks like making sure the exhaust port and header are lined up right or having the right amount of header wrap.
At the end of the day, we’re racing basic lawnmower engines so extra flow and what not won’t really make a difference