Upon startup my bike is firing off only the rear cylinder. On a bad day that's all i get. On a good day, once warmed up it will slowly studder and backfire and eventually the front may start to fire, then uppon further warming up (if firing on both cylinders at that time), that side will backfire upon deceleration. I've tried adjusting the low mix screw with next to no noticable difference. The carbs have been taken off and cleaned with new floats and needles and seals. Also attempted to sync according to the visual method while the carbs are off that was given in my manual, although i'm not sure how accurate that could be. Although if that was the issue, i'd think it would start to fire upon mid to full throttle anyways? But i'm no expert. Checked for spark and it seems strong, and the carb seems to be getting fuel, when i open the bleeder needle i get a steady stream. Anybody have a guess? Thanks!