Matelot,
Some years ago I brought my Mitsubishi back from the far East when I came back home. It had no hot air device for the air filter box as was apparently normal for that market. It used to suffer from carb icing in cold humid conditions and would run rough or cut out, even at cruising speed but more usually in town where small throttle openings were more likely. At such times, if you took the top off the air filter there was quite a lot of ice inside the venturi. Waiting for a couple of minutes for engine heat to reach the carb would melt the ice and all would be well.