Oldfeller--FSO wrote on 08/28/10 at 09:59:11:

Thank you, I am glad to hear that. Another thing I wanna know is, whenever I have the opportunity to access the spark plug, it doesn't seem as tight as left it the last time. It's not loose by all means but not really tight either. Is that normal on this bike for the plug to loosen up a little over time?

Serowbot wrote on 08/28/10 at 10:13:54:

I know, I hafta get me some.

An iridium plug won't give you better performance or gas mileage. It will last longer and on COLD startups, needs less instantaneous current and therefore starts the vehicle better. I noticed a significant difference in startup (half the time) by replacing the stock plug with the NKG iridium plug.

You can try the new Pulstar plugs. They work great in my car (better gas mileage AND more hp - the holy grail).

I have a 2005.  I did a search on NGK's website and it pulls up that the only plug for mine is a standard.  Thats with doing the search based on model, it calls out the 2005 s40 all by itself as an 656.  Then you do a search based on engine size, 650, and it pulls up the other year models.  Weird?  What gives?

I think theres "652CC" somewhere on the jug.