If you find that climbing through 5Kft MSL your RPMs are dropping off,
then
lean to max RPM for max performance of the engine and then bump it rich
just
a tad.

BT

Yes, you are quite right, density altitude is the key parameter. I
have one of those ancient Cherokees with the pamphlet-style POH.
There's not a lot in there, but they do say full rich over 75% power,
which as I recall, is about 8 kft density altitude at full throttle.

In any event, I've always been a bit conservative when it comes to
leaning, I tend to err on the too-rich side, thinking that I'm helping
the engine.


Mr Cherokee, I understand the problems with 1960-70s style POHs.
There have been some excellent articles in recent aviation magazines on
engine leaning, granted those procedures are best accomplished with added
engine monitoring instruments.

We fly a 1965 Piper Pawnee with 250HP (Lyc O-540) carbureted fixed pitch
configuration in glider towing operations. The airport is 2833MSL. Winter,
not many problems.. summer.. we are leaning as soon as we break ground for
max RPM. The mixture naturally gets richer as we climb after leaning due to
the climb, so we most always end up rich of peak and constantly monitor for
rpm drop with the richer mixture and then lean some more.

The mixture setting reached at altitude is left alone all the way back to
the ground.. lower power settings.. and is also used for ground idle if the
engine will idle without stumbling at that setting. Mixture is enriched for
go around or take off, until the engine gets up to speed and we are climbing
again. Oil temps are monitored, we do not have CHT or EGT gauges. Oil temp
in winter avgs about 180-190F, summer about 210F. We have two oil coolers
and change oil every 50hrs. We average about 250hrs per year on the engine
with weekend only operations.

BT