9 's will be a "colder" plug. meaning they will transfer heat to the head faster than 8's. so the 8 would be a hotter plug, and in theory burn off more gunk. so no, do not run the 9's if you don't have to. How much oil does it go through? if it was never in for the break in maint. at the dealer, the oil pump may still be turned higher than it needs to be. That is usually the cause of the gunk on a plug. Excessive fuel ( rich) would be wet and black, not really built up with gunk. That being said, mine always come out a little cruddy too, but most ppl check them after they get it in the garage, or after it has idled a while, or just loaded or un-loaded from the trailer. For a true condition, run it W/O for about a 1/4 mile or so, hit the kill switch, and hold the throttle wide open(gotta keep some fuel and oil in there to lube things) and coast to a stop. pull the plugs and see what you have for color... Nice cardboard brown is good. If still black/wet. probably a bit rich. Of course this depends on the temp. when you check it. Colder the air the leaner it will be. (air is more dense) so if it is perfect at 32 deg. it will be lean at 10. so I try to jet to the 0-10 deg. perfect, and let it be a little rich at 32. better safe than sorry.
If fuel injected, the computer should compensate for temp/ air density.
Jim
