Had a morning off today so thought i would take my 550f2 for a cheeky spin, the first outing this year! so checked the tyres etc and started it up, but only fired on 3 cyls, no 3 not sparking. of course its awkward to remove but tried it on the side of the engine and sure enough dead as a dodo. Ok so plugs do wear out but i have had this problem before with my 500/550 bikes, where after being stood for a while and even if it was running fine when last used, one plug decides not to play. I always use NGK and have very few miles on them so what is the answer, do i change brand?