@vickytulla, if I follow the chart, it falls within High Speed Glazing as you told. The Center Electrode, Side Electrode and Insulator, all three are with the same color (rusted color). This condition raised when I changed the mixture settings before the tour. Previously, it was all black and when I installed new NGK, right after the start, I opened and checked again (after a few 20-30 seconds and parked idle), it came as balck as the previous was. I unscrewed the mixture screw, one round and then checked again, it was totally unchanged[EDIT: with unchanged, I mean, I cleaned it like original and it stayed in same clean state]. Even it was same after 2 days. I thought I set it too lean, so I screwed it back one round. After that onwards, I am getting it like this [where as it should be black because I reset it to original setting]. Is it just because of overheating OR mixture needs to be adjusted? @silver_knife, which one you are using? Iridium?