P.S. You have the later carb on your bike & yes the washer is intende to be there on that model.

Regards Plodder

I also have a 59n model which also knocked and pinged like a goodun on overrun. the cure was simple, after making sure the carb was clean a new set of fibre reeds and shell advanced fuel was all it took.

mickh, thanks for your interest, I've heard that the shell higher octane fuel can help so i'll try that first, the old stuff can go in the mower.

I'll post the result as soon as I've done it

regards, Mike.