Which spark plugs are the best? I have a 19 HP Kawi. How often should I change them? I tried a while back to see if there was a Bosch +4 Platinum that would work with it, (looks interesting, thought I'd try it out) but the guy said that Bosch doesn't make a "+4" that would work with my engine. Anyway, which sparkplug (brand, type, etc.) should I buy when it comes time to replace it? Or do you have any comments on spark plugs?