SIMO

Hey, I got same sorta problem, missifre at 4000rpm, missfires if i put the foot to the floor. Coughs n splutters like a mofo on deceleration. Sounds way too rich. Drives fine at half throttle though. Got new splitfires, new plugs, clean injectors. Still doin it. Is a Safc the answer? If so what are good ones for R33 GTS-T. Also just moved to Brisbanes Northside n am lokin for a good mechanic on this side of town. Anyone know any?? Cheers...