The bike has been faultless till this year; on the way back from a long trip (2000 miles around sunny Spain)it blew an exhaust but after replacing it, the bike now, while ticking over will speed up and then slow itself down. All the relevant diaphragms are good, I´ve stripped and cleaned the tank, carb, vacuum pipes and air filters/expansion tank,cables are good, plugs are new and OK. Having got to the brick wall , I wonder if anyone out there has had similar symptoms?