I had a Harley that did that a while ago, it was put down to overheating by the dealer, when I got it back it still ran rough, the dealer denied anything was wrong, in the end I took it to Dynojet and had the ECU re mapped, it was transformed!!
Bearing in mind you are in the UK and its winter I doubt it can be put down to overheating unless you have recently been abroad?
Ian
