Hi Roger,

I then turned the mixture back to about 150 degrees ROP. The engine
was perfectly smooth. This is the way I used to fly it and the way I
know many pilots fly these planes. If I didn't look for or ignored
the lack of RPM rise in ground leaning, I could fly it this way for
months or years without suspecting there was a problem.

From this experience, I conclude that many or most engines out there
actually have minor induction leaks. This might also be part of the
reluctance of manufactures and shops to recommend LOP operation. LOP
any minor air leakage in the numerous hoses and joints of the
induction system will be a "problem" and something wrong with the
engine. ROP, minor leaks are not an issue and do not reflect on
either the builder or the repair shop.

Not until the engine suffers major damage due to one or more cylinders
running not quite as rich and therefore hotter as the pilot thinks they
do! Because this is what induction leaks and subsequent uneven mixture
distribution does. If your engine starts to shake before even reaching
peak EGT (mean), it can be concluded, that at least one cylinder is
running significantly left of peak under these conditions. The same
cylinder will, when operating the engine rich, be much closer to peak
EGT than the overall mixture.

(Lycoming would, based on findings of signs of overtemperature,
probably blame the damage on lean operation, though...)

I want my engine to run right and I now add to the list of LOP
advantages the fact that any problems with the engine will become
apparent early.

good point!

This is especially important to those of us who must
fly without and engine analyzer.

...where you wouldn't notice high CHT on just one cylinder, exactly!

regards,
Friedrich

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