I just got these roundtop SU's for my Z, they were on a L28 and worked fine, until i put them on mine. The car used to start up just fine, idles smooth, pulled hard on acceleration, then over a few weeks it started to idle rough like it had a cam on it, sluggish on acceleration, almost no power, and backfires like crazy when i lightly step on the throttle and dies. I tried tuning them adjusting the knobs on the bottom of the carbs, but doesnt seem to work at all. My car currently sits in the garage and does not start at all. A little help please? Thank you