Thanks for the suggestions. I tried a second plug and a different magneto but there was no change. I do remember this engine making very loud "staccato" noises that were normal but very loud. It's not worth spending any more time on. I'll change the engine out with an old Briggs and Stratton side valve. Good old standby's that don't cause me these mysterious troubles.
Last edited by sparker; 24/05/17 09:02 PM.