It was the dam valves!!

I went to the mechanics shop to get some small thing done, balance the carbs if my memory serves me right and I asked him about the increasing noise from the "valves". He listened and said it was nothing to worry about. I reluctantly accepted that and rode home. I had gone about 2 km when I was stopped at some traffic lights. All of a sudden, there was an almighty racket from the engine and I turned the engine off right away. The mechanic arrived with a van to pick up the bike and I had to get my wife to come 30km to pick me up. A week later I was told by the mechanic that 2 valves were bent. He said it was because of carbon build up. Mmm, I thought, why would there be carbon build up afeter having the top end overhauled and new seals fitted. He did not know.

So I irdered the parts and waited for them to arrive. When they did they were fitted but I wanted to know why it had happened.