Even the best of us forget how we were jetted from the previous season. Make sure the carbs are synced by insuring the slides all move at the same time, and that they all make it to the top of the slide bore. Clean everything thoroughly and reassemble. Do not install yet. Now is a good time to check the airbox out.
Mice have an abnormal attraction to sled airboxes.
They love to build nests inside and fine ingenious ways of getting in and out. Get out your flashlight and start looking around. Your fingers can help check the areas you can't see. Also check the overall condition of the airbox making sure that there aren't any cracks or big air leaks. Also check the condition of the carb boots leading to the cylinder.