Might be why out in left field here (wife says I am) but any benefit to running a hotter plug if your jetting is a little fat? How about a colder plug?
Thanks,

 

I wouldn't...

NGK Spark Plugs USA

 

Thats a great link!

Looks like you'd have to be operating well outside the designed specifications of the engine (force induction or something) to even consider needing to change the heat range.

 

But her a T shirt!

 

Nice link and info fz, think I just keep what I got.

 

Not always true. Think about it from the manufacturer stand point, which would you rather replace, a holed piston or a fouled spark plug. Usually they will be slightly cold if anything. Only way I'd ever go hotter would be if the plug actually showed it was "dirty", one range hotter might burn off the deposits properly.

We dealt with that on two strokes. Especially the small two strokes in extreme weather change. The little 50cc MB5 would range over three ranges hotter for cold weather, of course I actually eventually shrouded the cylinder, they ran that cold. The cold running could cause deposits on the plugs, fouling them, as we learned. Summer would have us at the coldest plug.

Four strokes are far more flexible when it comes to the plug heat range. And it is only about burning off deposits without melting the electrode, no performance gain other than having the plug run clean and continue to spark without shorting. I personally would not have need to change plugs because I'm not gonna ride when it's like 120°F or under around 30°F. Plus when I was riding the 650 in the winter when temps ranged from 30-70°F I blocked off one radiator to keep some heat. I'd do the same with the 250 if needed.