hi all i am finding that the cj8 s/plug is not doing the job it used to do perhaps it is the new type of unleaded fuel, i am finding the BPMR4A plug by NGK a much better choice,as for the fuel going stale,preventing the mower from running . What i have found is that the stale fuel will foul the plug, the mower will cough and splutter,backfire etc then stop and will not start again. the fouled plug will show a spark accross the gap when held against the cyl head, but will not spark under compression when plug is screwed back into cyl/head.perhaps a premium grade of fuel or a shandy of premium and unleaded might make the fuel last a bit longer . i mix oil at a 25 to 1 ratio using a premium grade 2 stroke oil low smoke. thanks for a great site well done graham