Hi Guys, I cannot fit new HT(spark plug leads) until the weekend. If the problem persists I will move on to checking coil and as suggested the Crank sensor.
It was the washing of the bike that convinced me to check my HT leads. They are exposed to water/heat consistently, you only need small cracks in the leads, which are invisible to the naked eye to interrupt the spark and reduce its power to the plugs.
Over several years you may not notice the reduction in spark.
Maybe it should be part of the service routine, say every 20,000 miles.
In the UK a lot of people change they rides every couple of years, so never see these problems.