Running Rich

I have a 2003 XR650R with the first level uncork as described in "The Wrench". I am runnig at sea level 80 F. I pulled the spark plug after about 150mi with the rejet and the plug is Black, with some black carbon buildup. I ordered the Uni Filter today to lean it out some. Would you also go one heat range hotter on the spark plug or wait and see what the Uni Filter does before you change anything else?

A different heat range, IMO is only for serious race engines. Use the "7" series plug that the manual calls for and you'll be fine. I tried an "8" series and it did nothing for me as I can see. First off what is your jetting and what elevation/temp are you at?

I am running a 175 Main Jet, Jet Needle(Honda 16012-MBN-641) Clip Position 3, Pilot Jet 68. Honda Competition Spark arrestor, Carburetor Insulator( 16211-MBN-640), Airbox Inlet Duct Caps Removed, stock air filter. Bike runs @ sea level/85F. All parts were installed at a Honda dealer. Bike runs fine, no throttle stumble, no back firing, starts easy. The spark plug is black and not the light brown that is normal.

Get rid of the stock filter and try a 172 main. At 85 degrees you should run a slightly leaner main unless your in sand all day long on the pipe. Sounds like the rest of your bike is ride up to spec. I had a black sooty plug until I put in a new one w/ the 172main and it was a nice chocolate brown, like it should be. :)

only make one change at a time makes trouble shooting much easier.

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