I have changed the gas and filters - It only gets rough after heated up - once cooled again it runs OK until heated up again Advice ?

Hi,
My first question would be "Do you have a Kawasaki FH series air-cooled V-twin engine on the machine?" The first few years had notorious ignition module problems. I had cases where I replaced one only to have the other fail. It got to the point where I campaigned (and won) to replace both modules with the newer modules under warranty. In many cases I could get adjustments on out-of-warranty machines. For some reason they can go for varying times but both seem to fail about the same time, like halogen headlamps.
Peace,
Clarke

I agree with Clarke, But I would also have the valve clearance checked.