Black sooty spark plug????

I am a proud owner of a 2001 WR426 and have been changing my spark plugs about every 4th outing. I have never messed with my jetting, it is the same as when I bought it new from the dealer.

I have removed my airbox lid, shortened the throttle stop and have removed the baffle. Would this be causing my sooty problem or could you think of something else I may need to inspect?

I live in the Midwest (Highland, IL just east of St. Louis, MO).

Thanks in advance for the advice. If I still have to continue to change plugs every fourth ride its still worth it anyway.

Mark Scheitlin

If your plug is sooty around the bottom of the threads, ignore it. It just means your cooling system works.

Look at the ceramic cone that comes up almost to the center electrode. If that's darker than medium tan, you're rich somewhere and either or both of jetting and accelerator pump mods will fix it. If its bone white or close to it, its too lean, probably everywhere.

Look at the bottom of the 'Jetting Q's' article for jetting tips. Look for BK mod or for P38 for two ways to keep from being too rich from accelerator pump overkill.

You should never have to replace plugs (well hardly ever).


repost or PM me if you need more help.


I was having the same problem on my 2001 426. I was fouling every 4th ride as well and my spark plug was black and sooty. I was also having mid-range sputter. With some help from the guys here at TT, I discovered that I was running rich on the needle jet. I changed my needle jet clip position from 4 to 3 and I haven't fouled another plug since.


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