I'll bite whats a Silverstone ?ND W31FN all day long, backup plug would be Silverstone.
Silverstone is made by a company called Beru out of the UK and sold through Nology. I have to look on the box for the number but they only make 1 plug that fits a flathead Briggs. Solid silver core and a much stronger spark than a standard copper core. EC was very high on them back in the day. Have never manged to foul one personally. They are not cheap though and getting harder to find.I'll bite whats a Silverstone ?