Firts, i'd switch the plug wires, see if it switches sides. If so, its the coil. Simple fix.
If its not the coil, its going to be a carb issue of some sort, regardless of them being new or not. You should check a few things
1. Floats, one side could be off- check, and then double check.
2. Carb sync.- pull air cleaner set-up, look in the back of the carbs to make sure the slides are moving at the same time.
3. Air Screws, make sure they're evenly set.
4. Choke tube, its wicked important to have in place.
Good luck, let us know if any of these help!