Originally Posted by FlyingForFun
TotalBeginner has read his POH, and told us that it does not recommend leaning below 3000'.
My bet is that it doesn't say that at all, or that it's been written by somebody who has misunderstood the engine manufacturer's recommendations. The Lycoming advice has always been that you
must lean above a certain altitude to prevent the engine running grossly over-rich. Unfortunately, this advice has evolved through Chinese whispers into "you mustn't lean below x thousand feet", which is total garbage.