Burning old gas isn't the best of ideas. I had about a quart of 15 year old gas I needed to dispose of. I poured it in a metal pan and lit it up. Smoked a little more than I expected (a lot more) so I had to put it out before the neighbors got worried. I live about a block from a fire station. In the end, I just mixed it in with some old oil and let the recycling station deal with it.