I was just thinking , if you had any moisture in the carb floatbowl and it's below freezing (27*) that moisture maybe turning to ice. Also cold air/with humidity rushing thru the venturi (throat) of a carb could cause a phenom called carb icing. Since you can't heat the air prior to it entering the carb one has to learn to work with it. Change your fuel mix a tad using the screw or enrichener ****.