sounds to me that you are too lean, when the weather turns cold the air is more dense and needs to be richened. Just remember that when its winter richen the hsn. going thru plugs and poor performance could also be a bad rear bearing. Someone said that you should check for pitting on the piston from predetonation, well it could also be pitting from the rear bearing coming apart. I have had to have the hsn out 4 turns in colder weather to make it run ok. Hope this helps