Another Question About Leaning

I also have a question about leaning, but decided it wasn't applicable to RICHDALE's thread.

I have a Cherokee 140, normally aspirated, fixed prop with an EGT. I was taught to climb to altitude and set cruise rpm. Then start leaning the mixture and watch the EGT. When the temp. peaks and then starts to cool again I should then enrichen the mixture until the temp. goes back to 100 degrees below where it peaked. Does this sound about right?



  • Yes. At high altitudes you can even consider 50 ROP.
  • Thanks most kindly for your response, flyguydon. I appreciate the help. As a new pilot, it seems the more I fly the more I find out how little I know. It's nice to know I can come depend on you experienced folks to help me out. I hope to become experienced enough myself to return the favor to others.

  • If a 140's POH says anything about leaning with an EGT, it says the same thing as all the other Piper POH's: "refer to the Lycoming Operator's manual." Those, of course, were not supplied with any of our aircraft.

    Mike, Lyc calls the technique you're using the "Best Power" setting. For "Economy" you leave the mixture set at the peak EGT temperature. You'll lose a few knots but fuel burn will be down. Either setting is OK.
  • Thanks JoeB and PropFan. It's nice to know I have the right procedure. I don't want to foul the plugs or burn out the valves. Much appreciate all of you guys for helping.

    PropFan, I'll download those reprints and look them over for sure.

    JoeB, I probably better stay with the "best power" setting. Little 18W is already pretty much a fuel miser (8.5 gph at 75% and full rich) but she's a little club footed when it comes to speed, heh. Got a good heart though and I'm rarely in a big hurry. Just love to fly.

    Thanks again all.
  • Second the notion of getting the Lycoming reprint info. I believe there's a general one on leaning that's pretty informative and you should be able to find model-specific data on their website as well.
  • Even without the EGT on a 150/160HP carb fed engine it is real simple.

    Level off. Set the RPM where you want for cruise. Get established in the cruise. Slowly lean until it stumbles. Slightly richen it back up until smooth (about 1/2" on the mixture). Fly it.

    Be aware any altitude change will affect the setting. If you are going to climb... richen it up (but if over say 5K you do not have to go to full rich) and climb... once level repeat the above procedure. If going lower, richen it up and repeat the above procedure once re-established in a cruise.

    As an example, if you lean for cruise at say 8K and do not richen it up and descend... your engine will get real lean beginning at say 5K and will "stumble" and really get your attention at some altitude below that... :)

    This is not rocket science. Most/many planes like yours do not have any EGT on them. EGT becomes more important on fuel injected engines as they will run smooth and don't give the "stumble" to guide you as you lean them. This makes it possible to lean to peak or even lean of peak and not really know it. For example, my Arrow will lean beyond peak and run smoothly until it is hardly making any power at all. Carbs will not tend to do that.
  • Flyguydon's "no-EGT" procedures are spot on and are probably more valid than relying on a single EGT probe, which may or may not reflect what's going on in the leanest cylinder. It took me a while, though, to get comfortable with intentionally making an aircraft engine run rough in flight. Now, it's no big deal, and I enjoy the process.
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