Guys & gals.
I've done about 750 miles this week in our wonderful wet/foggy (delete as appropriate) weather.
I had to fill up 4 times with petrol (all from the same station)
Yesterday I filled up with petrol for a trip down to Poole and I had a misfire for a few miles - not immediately but after about 20 minutes of riding.
I had to fill up again Today - same problem on the way to Salisbury - not too bad so continued to ride. Came home tonight and it was fine - full power, no misfire at all???

Symptoms - lack of power in relation to revs, seemed to clear when high revving and then re-appeared when low revving / lack of gas / coasting.