Posted for "Rick Lafford" <gliderguy89@earthlink.net>:

 Gee Scott, I fly a much slower plane and spend more time taxiing that you.
 Try flying a Pawnee towing gliders all afternoon. Takes maybe 3 minutes to
 2,000' and then back down for the next victim. Ground time typically equalls
 flight time.
 
 Once slowed down and taxiiing, mixture comes back to a visual position that
 will not allow the engine to achieve much more than a fast idle. The
 difference in plug fowling and the color of the oil is dramatic, not to
 mention the reduced fuel burn. We change oil at the 25hr. mark because the
 engine (O-540) lives a tough life. Without leaning on taxi, the oil actually
 looks silver. With leaning it's the more typical carbon black.
 
 One other difference when leaned is that the engine doesn't develop that
 typical 540 sycopated idle.
 
 Even being able to show these dramatic differences, many old heads, over 75%
 of our tug drivers and some not all that aged, consider the practice
 dangerous and subscribe to the Full, Full and Full school of mixture
 management.
 
 Rick Lafford, CFIG
 Tug Puke and Legacy someday
 Dansville, NY (DSV)
 
 "Touch that mixture knob and you're bound to ruin that engine."


"""
  To me, 15% to 20% makes it really worthwhile to operate the engine
 properly and, like many others, I aggressively lean during the taxi phase -
 generally, the big pull to a known visual position of the mixture knob, to
 be fine tuned when time is available.  I do this shortly after engine start
 and as I pull off the runway after landing (assuming I am able to leave the
 runway under power).  If it matters, the placard on the mixture knob (Push
 Mixture Rich) has been thumbed to an almost unreadable state.  I may have to
 placard that placard as inoperable.
"""