We used to go to Brands Hatch a couple of times a year from the West Midlands and used to stop for a break somewhere north of London. There were two of us on Commandos and we both noted that our bikes ran noticeably smoother after the stop. The difference was enough for both of us to notice and comment. We hadn't refuelled, just stopped for about a half hour. We never figured out why but it happened on long trips often.
Ian