I just found this on the internet...what ya think??
READING SPARK PLUGS - Determining proper fuel mixture by inspecting the color and condition of the spark plugs can be very helpful in situations where the engine is being operated constantly at full rpm under full load. "Reading plugs" for perfect fuel mixture is very common where the engines are nearly always run at full rpm and full load.
To get an accurate plug reading on an engine, a fresh spark plug should be run in the machine for 3-5 minutes at full throttle/full rpm on a relatively clear track. At the end of the full throttle running, the throttle should be chopped and the kill button pushed simultaneously (called a "plug cut"). If the engine is run at partial throttle for even 3 seconds after the full throttle run, the plug reading will be invalid.
After the full throttle running, and the plug chop, a combination flashlight/magnifying glass must be used to view the carbon deposit at the base of the porcelain (down inside the spark plug where the porcelain insulator and outer steel spark plug casing meet. A ring of dark brown at the base of the porcelain denotes ideal fuel mixture, light brown is lean, and a ring of black is over rich. This is the only area of the spark plug that accurately indicates fuel mixture. Furthermore, this reading only indicates full throttle fuel mixture. No part of the spark plug can indicate low speed or mid range fuel mixture. The upper part of the spark plug porcelain (by the electrodes) is often very light or white in color, however this coloring is mostly affected by additives in the gasoline and oil. The coloring of the end of the porcelain in no way indicates appropriate fuel mixtures of any throttle range
