Thanks again.
The problem seems to occur after a sustained period of cruising speed (i.e 70 mph for an hour or more) and coming into an urban area. It then coughs and splutters for 5 - 10 minutes during which time I have to ride the clutch and keep the revs up. Then it settles down again.
I shall have a look at the ASC at the weekend and run it on quality petrol for a while.

The problem seems to occur after a sustained period of cruising speed (i.e 70 mph for an hour or more) and coming into an urban area. It then coughs and splutters for 5 - 10 minutes during which time I have to ride the clutch and keep the revs up. Then it settles down again.
I shall have a look at the ASC at the weekend and run it on quality petrol for a while.