I agree, I did mine on my 300r at around 110 hours.......the plugs looked perfect, gap was perfect, but motor ran noticeably crisper and idled even rpms in gear after changing them. Keep in mind the 300 hr service is 300hrs or every 3 years. Fuel quality might also be an issue for you if you're only doing 25 hours per year. Do you run the motor hard ever?