Just to let everyone know that my problem was ME!.....filling up with Diesel!! I have a diesel car and the smell of the diesel did not ring any alarm bells with me. I stripped the carb several times and then bought and fitted a new idle jet, - all to no avail. Eventually had the bike transported to my (v. good) local bike garage who immediately smelled the diesel. He simply drained the tank and filled with petrol. It´s been great since.