Originally Posted by
Rhino25782
From my understanding, the "fully rich below 3,000 ft" applies to the climb only and anything else is just a sort of safety precaution in the training environment?
Yes unfortunately in lieu of actually teaching people how to properly lean the schools dumb it down to a one size fits all SOP
I tell all my students to go to the Lycoming web home page. They have a great section called Lycoming tips. I also encourage pilots to get a copy of the Lycoming engine operating manual for the engine type in their aircraft.
To answer your question. Lycoming is
unequivocal about leaning. You can lean your engine at
any altitude as long as the power it is developing is less than 75%. For climbs to higher ( eg above 5000 feet ASL) altitudes at full throttle leaning
is mandatory to achieve POH book performance.
I lean in cruise at all altitudes all the time. It is actually better for the engine and it saves gas.
As for technique on your average trainer/tourer that has a carburated 4 cylinder engine pull the mixture until the engine starts to run rough then slowly enrich until the engine is smooth again, job done.
When leaning it should take about 10 seconds of slowly moving the knob from the full rich position to when the engine starts to run rough. Leaning faster than that will usually cause you to overshoot the actual moment when the engine starts to run rough indicating a too lean state.