But you still need oil. If you run it lean, you will have less oil, and the engine will run hotter. Running hotter means more friction. Don't you need oil to reduce friction? You don't want the engine to run lean at all. It is better to be rich, than lean, but ideally, you still want to be just slightly rich. Don't forget that that piston in your engine is aluminum, and it doesn't take much to damage such a soft metal.