The only way to make a spark plug turn "chocolate brown" these days would be to get in the "Back to the Future" time machine and buy sone leaded gasoline! The old "white/gray/ chocolate brown/black" method of diagnosing fuel mixture also stopped being accurate, somewhere in the 1970s when leaded gas went away. The lead additives were what made the plugs change color.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!