I had a B/S engine on a snow blower and it never started when it got colder. I found out that I had a crack in the head gasket and in the cold weather this would expand and make it hard to start. Some 15 years later I used that same engine on my long splitter and had a weak spark. Thought it was the coil and the repair shop told me to clean my points. Sure enough that time it was the points. This summer my lawn mower was starting hard and I found the key in the flywheel was off just enough to make a difference.
I'm from the old school and always try to pre-heat my little engines. When we flew our airplanes in the winter, there is an old saying, pre-heat the engine when you need to wear a jacket. Many time we where were not around electric so to pre-heat the engine we took a weed burner, the type that connects to a LP tank. We would tarp the engine, took a 6 inch stove pipe about 4 feet long and put one end under the tarp and the burner in the other end. The natural draft would be enough to keep the stove pipe cool enough and yet heat the engine. We used this idea to pre heat our log splitter for many years. Even now I pre heat the new Speeco when it gets in the 20’s. I tarp the splitter, and heat the splitter with my LP heater. It gives me time for an extra cup of coffee and allows the fluids to warm up a little. Even now I think about the 4 wheelers and how to pre-heat them when I’m on the lake fishing when it’s -18 below.