This sounds like a possible icing +/or dirty fuel condition.
You could , + probably do, have water in your fuel, if so the water could have migrated through your fuel system and finally frozen in your fuel pump and/or carb float bowls + jets. If possible get the sled in a warm garage over night, drain every drop of fuel out of the sled, clean your carbs again, get some premium fuel from a busy gas station, add some gas line anti freeze[Isopropyl alcohol] and try it again.
Also check your fuel filter in your tank, and ensure the fuel pump pulse line is attached properly.
Hope you get it sorted out!
With the ethonal added fuels we have today they suck moisture out of the air[hygroscopic] and accumulate in the fuel, hence creating all kinds of issues for sub zero use, both in our cars + our toys.