well first off, 2 1/2 gallons is more than the life expectancy of that motor. in my experience, a properly tuned engine will go through a gallon to a gallon and a half before the sleeve/piston are junk. For cold weather running, id recommend buying a spare cylinder head. use a hack saw to cut off some of the cooling fins, about 30% of them. Then, if you have access to a machine shop, or you can use really fine sandpaper on a piece of glass, remove some material from the bottom of the compression dome to lower the compression. shave about 20-30 thousands off. this loss of compression will be compensated for by the denser colder air, and the low temps will be brought back up by the modified cylinder head, thus eliminating any adverse effects of cold weather running.
-Alex Galeczka