Because the OP asked about mixture questions, literal person I tend to be, restricted my answer to that issue. For the threads (especially on plug 2) to be as discolored as they are after only 90 miles, IMO, the plug is too hot. Ideally only the first two threads should be discolored. IIRC, the farther a plug's electrodes and porcelain extend into the combustion chamber, the hotter the plug.