Spark Plug Service Interval

I missed the factory 7,600 mile spark plug replacement interval by about 2,400 miles. First go round I usually try to keep with or better the scheduled maintenance (that I can do) but being on the road between 5,500 and 10,000 miles made it a little difficult to fit it in. So I got on it as soon as I got back. In process of changing the plugs, I also replaced the air filter element which is about 1,400 miles before the factory 11,400 service interval. My thinking there is that I was close enough to the service interval to avoid having to rip the tank and air box off again in such a short period just to put in the filter.

Anyway, the bike was running perfectly fine going into this maintenance, as well as after. The thing runs like a dream. So far this summer I’ve had many 500+ mile days in triple digit temperatures and the bike just keeps rolling smoothly without a hiccup.

Here’s a look at the plugs removed at 10,000 miles. They are NGK CR9EIA-9 Iridium Plugs. They look like they could have gone another 10,000 ... and I have no doubt that they could have.

Here’s a look at the air filter element removed (bottom) and new one (top).

The service intervals on these maintenance items seem pretty short, but they’re consistent with the little 650 Versys that I had previously (perhaps a Kawasaki thing), which also used the CR9EIA-9 Iridium Plug. However, they’re way shorter than my Yamaha Super Tenere and several other models that I had before that, which was 12,000 miles for the plugs and 24,000 miles on the air filter element iirc. 

Personally, I’d thought that these Iridium plugs were supposed to be harder to provide longer lives and be more tolerant of leaner run engines. They certainly cost more. I paid $9.99 each for the Iridiums where a typical plug may cost $2.50 -- $3.50, and these particular plugs are not fully Iridium. The three components are Center Electrode=Iridium, Ground Electrode=Nickel, and Core=Copper. In addition, we know that motorcycles run much leaner (which equates to hotter) and under much more compression (also equates to hotter), which taxes spark plug life.

Irrespective, it's fairly clear that the 7,600 replacement interval is extremely conservative. The plugs that were removed at 10,000 miles indicate minimal wear during the hottest and most demanding time of the year. I've had many triple digit temperature full-days and am running my higher viscosity oils. I suspect that doubling the factory cycle (around 15,000) is probably a better interval and will likely be going with that.