I live in northern Michigan. When I attempt to start tractor after it has been sitting a few days it will only start if I warm it up with my salamander Kerosene heater for 10 minutes or so. I point the heater at the tractor and let it blow warm air on it for 10 minutes. Then it will start right up. I have replaced the fuel pump, added dry gas to the tank and replaced the fuel line flow valve. Battery is new. I do not have this problem in the summertime. Any suggestions will be appreciated.