My 2200 TC doesn't do many miles nowadays but, after a 30 mile run to clear the cobwebs, during which I noticed slight misfiring under acceleration when warming up, I took the plugs out to check their condition. To my surprise, 1, 3 and 4 were the expected colour, but 2 was very sooty (incidentally, the misfire went away once the engine was hot). I have a couple of Colortunes from earlier motoring days and put them in 1 and 2, then into 3 and 4. Cylinders 1, 3 and 4 were the correct shade of Bunsen blue, but 2 was distinctly yellow (rich mixture). I appreciate the old Colortunes, which go back to leaded days, are not accurate but they seemed to confirm the visual inspection of plug two. Any ideas guys how the mixture to three cylinders is OK but one is rich? For info, the car is running on relatively new super grade fuel with lead additive, and ignition and carb settings appear OK.