Reading spark plugs is a futile effort since they quit putting lead in gasoline. The white / tan/chocolate brown /black colors we used to look for don't happen any more- - - -plugs go from almost white for any normal fuel mixture to black and sooty when the mixture gets overly rich. Black and greasy still indicates oil burning. You're about 40 years late with that tuning method, which is why I mentioned a 4-gas analyzer, preferably one that can be rigged to monitor mixture during a road test. I ran a test like that on a 600-mile round trip to an advanced tuneup seminar sponsored by Snap-On about 20 years ago, but the doofus assistant principal at the school where I was teaching auto mechanics decided to clean out some file cabinets over spring break one year, and discarded the files, along with documentation of hundreds of chassis dyno and engine dyno runs. He was not welcome in my shop for a long time after that!
Jerry
