Thanks for the comments guys. I did suspect that the pipes could have had an impact. Top end rebuild and new battery are on my list of things to do. I had it on the dyno only the other week as a health check. If the Ace Cafe meet hadn't come up, I would have drilled the airbox and taken it back for a rejet on the dyno.

You live and learn I suppose. Maybe it was the pipe, maybe it was just it's time. Whatever, it still leaves me with a top end rebuild to get done.