96 Johnson, 60 hp 3cd, engine won't run under load when put the throttle to it in gear, rev's high in new, but does cough n sputter alittle. I checked fuel line, fuel good fresh, mixed correct, fuel getting to carbs, Pulled plugs, 1 okay, but two were blackish and oily, haven't got to checking spark yet, as it happened on water. (As usual it ran fine the day before), any thoughts on this. (sorry no serial/ model I lost the number, need to go look again) 