I have a lawn mower that has not been run in over a year. I bought it new and I haven't run it but 3 or 4 times back over a year ago. Now it won't start. Well, it will start when I spray carb cleaner into the carb and it will stay running as long as I keep spraying the cleaner into the carb. I am wondering if it is the gas I am using? The mower was completely empty and I put in gas that I had been keeping in my garage for over a year. Does gas lose its potency after being stored for a long time?