Also the guy i get my lawn mower repaired by swears by this stuff:
STA-BIL 22208 Fuel Stabilizer - 8 oz. : Amazon.com : Automotive
He says that 90% of is business is fuel related because of the seldom use or long term storage of gas in containers or in small engine machines, like generators and lawn mowers. It keeps the fuel system clean with regular use and keeps gas from breaking down during long periods (like winter). I used it all last year and stored my lawn mower properly with it and it started on the first pull this year (without starter spray or anything).
You just add a couple drops per gallon in your gas can during regular use. For winter storage you add like a ounce per gallon and let your mower run for 5 or 10 mins so that it cycles through the engine and fuel lines.
I have also heard other good things about it from other people and the internet. If you buy some get a small one because the stuff will last forever. Its like less than $5 at Walmart.