Generally, the 750 and 50/550 K models were all too rich, so much so that they had plug fouling problems in the summer. But, they run quite well in the winter! Remember that these are small-bore, low-specific-performance engines, so the changes in the carbs are relatively unneeded. I have found, though, that running with the Vetter lower in the winter, which enclose the airbox, does improve the MPG and early throttle response in cold weather.
I also found the Transistorized Ignition has almost completely removed the cold-run stumbles it has always had. I am attempting to ride it into colder weather this year, just to see how far this effect goes down, so long as I still have this short 7-mile commute. It was always that I had to baby it along with the choke for the first 2 miles or so: now, by the end of the block, it runs perfectly, even below 35 degrees.
At continuous sub-zero riding, a 5-more mainjet on the 750 was helpful, but that was a long time ago, for me (1970s). Now, my lower limit is 30 degrees, where ice shows up everywhere around here. That's more about safety than engine run quality, though.