stopped revving out cleanly?

[2fiftosR]

went riding yesterday bike ran well for around 1/2 an hour. switched her off for 10 or so minutes and when i started riding again it began breaking up on the top end (not revving out properly)?
i have been running it on the rich side but it hasnt been an issue till now. not sure if the plug could be the cause, just looking for advise before i go dropping main jet sizes..

[86250rrider]

do a plug chop and see how it looks. im not sure where your at ,but here in pa. the air gets better in the fall.my plug runs a tan-light brown to keep it crisp. MORE INFO :D