[aljeann]

dont know if i bought the right sparkplug for my crf250x 2006. the manual says its an NGK (IMR8C-9H) but the sparkplug that was sent to me was NGK (IMR9C-9H) is the latter better or better to use the stock sparkplug

[Monkeywrench]

I think either the owners manual or the service manual (maybe even the parts ordering manual - I can't remember where I read it) has only 1 comment about the optional plug, which is something like, "for extanded high-speed riding". Maybe a plug that takes heat better? Last time I replaced mine I chose to use the same one you just got (the optional plug) -- didn't notice any difference... just a different number, maybe with thicker porcelin walls (heat dissipation??)
Not positive what's different.

[Monkeywrench]

I think either the owners manual or the service manual (maybe even the parts ordering manual - I can't remember where I read it) has only 1 comment about the optional plug, which is something like, "for extanded high-speed riding". Maybe a plug that takes heat better? Last time I replaced mine I chose to use the same one you just got (the optional plug) -- didn't notice any difference... just a different number, maybe with thicker porcelin walls (heat dissipation??)
Not positive what's different.

[124]

The number you are referring to is the "heat range" of the plug. An 8 burns hotter than a 9, a 7 burns hotter than an 8, etc, etc...

You may want to use the 8 if you notice the bike bogging or losses throttle response. It shouldn't hurt anything using the 9 though...