Might be totally off the mark, but have you ever come across "petrol poisoning", I run a high performance motor bike that I use very infrequently, costs me a battery and set of plugs every year, you can never see anything wrong with the plugs other than being wet from fuel , despite cleaning the beast will not fire until new plugs are fitted,according to my motorcycle mechanic, ( I dont touch motorcycles), this is a common problem, cannot validate over and above my experience?

Tony