Sea-Foam.
Depending on the size of the tank put a 1/4 - 1/3 of the can in your tank when you are storing it, and then run it for a bit so the Sea-Foam treated fuel gets into the Carb+bowl.
My Snowblower is 10 years old now, mower is 9, I do this to them (and fog the Engine) and so far have had...