[HighFLyer]

On leaning, the most common thing I have heard is to only lean when your density attitude is at least 3000 to 4000 feet. And this is only necessary when cruising for long periods of time. A short trip at 3 to 4000 does not really nessicitate leaning, and the chance of accidently leaving it too lean can become a serious danger.

What you heard about running an engine too rich seems a little strange to me. As far as I know, the only danger of a too rich engine is fouled plugs, and if you are running 100LL this shouldnt be a problem. Your fuel burn might be a little over what is expected if you dont lean out your engine, but this wont hurt at thing.

My advice is to lean out your mixture any time you plan on flying above 3000 feet for an extended period. Or if the temperature is extremely high and the air is very dry, then you may benefit from leaning at lower altitudes. Hope this helps.

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