Fuel for your lawn mower or outdoor power equipment must meet these requirements: Gasoline with up to 10% ethanol (gasohol) or up to 15% MTBE (methyl tertiary butyl ether), is acceptable. Some fuel stations are now selling gasoline with up to 15% ethanol.

It will be fine. The gas will clean the engine. Drain the oil/gasoline mixture leave it empty for a day then fill it with oil. Please replace the oil filter as well. John deere sells a service kit that has all you need to do the job. I work on engines for a living. Have poured small amounts of gas into an engine before to help clean sludge build up. The Family Handyman automotive expert, Rick Muscoplat, will show you how to change lawn mower oil. Changing your oil for a lawn mower after every 25 hours of use will keep your engine healthy. Find out the best way to change oil for a push lawn mower in this video, including how to drain oil from a lawn mower.