(Rick Durden) wrote in message om...
John,

Specifically, you should not be leaning if your engine in making 75%
power or better.

Not necessarily so. It is perfectly okay to lean at 75% power, the
manual for your airplane has a fuel burn for 75% with lean mixture.
In fact, if you don't lean when operating at 75% with that Lycoming,
you will significantly reduce your range and endurance and possibly
foul the plugs. www.gami.com has a good discussion of leaning and
what's going on during combustion. It may be perfectly okay to lean
at power settings above 75%.


OK, perhaps I didn't include enough information. For the Lycoming
engines found in most common Cessnas & Pipers, Lycoming manuals
usually have caution against leaning above 75% power. Perhaps I
should have reworded my comment above to read "76%" or "75.5%".

I've seen exhaust valves from engines that were run at high power
settings while leaned to just below peak. They were not pretty (and
would not hold compression).

John Galban=====N4BQ (PA28-180)