I've had decent luck with a product named StaBil 360. You add it to ethanol laced gasoline and it keeps rubber parts from deteriorating and the gas from going bad. Actually it is probably most noticeable in a lawn mower because you only have one cylinder so starting can be more problematic if you have weak gas. About 3 years ago I took 3 small jars and put gas into them...one month apart. I posted the results here but as I recall they were in with another post. What I learned was just sitting for one month made the gas turn sort of orange and smoke a lot when burned. 2 months caused it to be a little worse and 3 months made it pretty honey-colored and it really smoked a lot when burned.
