Back in the 70"s when I worked on motorcycles, I had a service manager who had a KZ 650 Kawasaki that would tick on and off at idle sometimes. After a full service it still ticked so he removed the valve cover and ran the engine. What he found was that one of the cams was every now and again moving back and forth and making the clicking noise. He checked the end play on the cam and it was on the low end of the scale. I watched this happening, the cam would be steady at idle then move side to side Very fast and then stop it"s side to side movement, so if you can check the end play of your cam do so.
