My older model Murray 21 inch is chewing thru gas. I only use high test gas and oil mixture. It is a few years old but I was wondering if there is something I can do to prevent this? There is no smell of gas in the garage so I'm guessing it isn't leaking that I can see or smell. I run quickly to do my driveway and usually I can get three driveways done before the full tank is empty. Any ideas?