I've used NGKs for many years/decades in my jetski, scooters and karts but as of last year I've switched to Autolites. I think NGK went thru a phase where their plugs were easily fouling up and going bad. (But that was 2 years ago) I found a box of B6HS plugs that are at least 10 years old. They are the ones with the gold/yellow coating. I've been using them in my bike. I know they are a colder and longer plug but it works fine and I have a little bit more bottom end.