Greetings:
Sorry, I just don't buy the winter lean thing. Denser air is being sucked through the venturi, to be sure. However that will have the effect of increasing the pressure gradient at the fuel inlets as well. Fluid dynamics are hard to predict, but the net result should be a higher fuel draw at least partially compensating for the more abundant oxygen.
I suspect your boggy running is more likely the result of carb icing or an engine that simply can't reach nominal operating temperature.
Consider raising your needle before you swap jets. If that fails to improve things maybe that towel should go over the cooling shroud....
![Smile :)](./images/smilies/icon_smile.gif)
But watch your engine temperatures carefully.
I once owned a first-generation Mazda GLC. Little 1300 4 engine with a thin-walled aluminum block. Driving at highway speeds in -35 degree weather, the engine practically stopped a few times until I discovered that covering 3/4 of the grille with cardboard solved the problem. Trucks & school buses up North have zippered grill covers to achieve the same ends.