POH manuals always tells to use the voice of the engine as a reference. (Which complicates things a little bit since carbs and fuel injected planes have different "reaction times" for each cylinder)

But how do you lean the mixture without using your ears? How do you lean mixture with only the instruments as a guide?

Lets assume we have a brand new C172 Skyhawk

  • 2
    $\begingroup$ Depends what instruments you have... Does it have a CHT? Single or per cylinder temp gauge? Manifold pressure gauge? Or just tach? It's actually really easy to tell by paying attention to the engine. As you lean it out the engine will noticably get rougher. $\endgroup$
    – Ron Beyer
    Commented May 25, 2019 at 12:49
  • $\begingroup$ @RonBeyer lets assume a brand new C172 skyhawk $\endgroup$ Commented May 25, 2019 at 12:57
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    $\begingroup$ sweetaviation.com/leaning-procedures $\endgroup$
    – abelenky
    Commented May 25, 2019 at 13:01
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    $\begingroup$ Related: What appears on EGT Gauge if the mixture is rich or lean? $\endgroup$
    – user14897
    Commented May 25, 2019 at 16:25
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    $\begingroup$ Are new C172s fuel injected? They could in theory run Lean of Peak for lower fuel burn & cooler cylinders if the injectors are evenly matched. $\endgroup$
    – CrossRoads
    Commented May 26, 2019 at 4:48

1 Answer 1


The procedure varies depending on the engine instruments in the panel. Here’s an good explanation using the EGT probe on a Cessna 172.

And here are the manual pages from a Cessna 172SP that explains it.

[Lean Cessna 172SP - 1[2]

Lean Cessna 172SP - 2


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