if you have a buddy that has a banshee,ask if you can try his carbs to eliminate whether your left carb is good or not.if it does the same thing you know it's not your carbs,check your timing or the electronics that screw on to the top of the carbs make sure that current is working and you dont have a short their,and go through your entire harness to see if anything was spliced and came apart and last thing get a compression check a.s.a.p could be you need pistons.