I have the service manual and the 'Bible' of dirtbike tuning (E. Gorr's book) for my 1997 RM125. I ran on the same plug for about half a summer, a platnium BR9EVX which is what the bike came with. It gets hot around here... but we'll guess the avg tem was about 80 deg. It had been steadily cooling but the bike still ran great.
I fouled it when I left the choke on by accident and rode it. Then, I took a trip to higher altitudes and colder temps. The track was CRAZY muddy and after I dumped the bike a few times the plug fouled. Since then, it has kept fouling plugs. Coincidental? Or is it possible that the colder temps are helping? I moved up one heat range (8 non platnium) and currently am at 7 but that's a newer plug, I haven't read it yet but will today.
My question is, will I most likely be able to get by if I move the needle down one position? I'm never at WOT anyway, still learning.
And while we're at it, how does the choke work on this carb? It's a Keihin. PWK? I beleive.