Re: Small Engines cold air and Performace.
Yup... just look up cylinder head temp gauge on ebay... they run off a small sensor that goes under the spark plug like a washer or better yet, like a ground wire... These are fairly cheap but most of them need a 12 volt source to work.
I'm not totally sold on the spark plug heat range theory for cold weather since the air is more dense, thus leaning the fuel mixture, the last thing ya wanna do in a lean condition is put in a hotter plug.
But really, even with all the temperature swings in the wintertime in some places, do you see everyone changing their plugs and rejetting for the cold then changing back for the warm weather in their cars, trucks, buses, motorcycles etc? Nope... everyone just drives them. Some people block off part of their radiators in the winter, but that's about as far as they go with that.
You *can* do all that for the weather extremes, but it's typically not necessary unless you're just looking for maximum performance all the time, or on race day.