My /6 is a gas pig when it's cold outside. Why?

More advanced timing may help quite a bit. 5 to 10 BTDC should be no issue.

Make sure you are using a 180 thermostat. I used to have to block the rad with cardboard deep in winter in northern Indiana. The /6 has a large block area on the outside, so tends to run cold very easily.

Then adjust the choke leaner a bit at a time until it won't run well dead cold. If you have the heat well type, pull it off the manifold and you should find a small adjustment on the spring pivot inside the heat stove housing, and it will have L and R marked for leaner or richer. Loosen the nut and turn the mark a bit towards L.

Also, be sure the float level is right on spec. That effects all carb operations, including the choke operation. It might be a bit high in your case. If you change this, you may need to reset the idle mixture, and see how it drives in other modes, like the transition from mild to moderate throttle opening.

Mileage is going to be less for sure nor matter what with the choke on. A warm up for a minute will help.