: I'm running in my overhauled engine - 4 hrs - all a full rich.

: I don't understand why you would want to operate the engine without
: leaning. No recommendation I've ever read about post-overhaul break-in
: ever included anything like that.

For breakin (4 hours is a good minimum for when most of the breakin should
have occurred), you absolutely need to run at a very high power setting. High cruise
(~70%) is a minimum, but I've seen recommendations of 85% or so as well. At those
power settings, you'll need to have a very rich mixture to:
A) Prevent major damage from detonation
B) Keep the engine cool (CHT cooler than "normal" preferrably)

I've got an EGT in mine (now well broken in), and in a long climb I'll lean to
maintain EGT I get at takeoff (1400 on my plane). If you don't have that, you're
better off leaving it full rich while you fly around for a few hours at 85%. A few
hours at wicked rich isn't going to hurt/dirty anything... just reduce power (70%)
before landing and lean it until it wheezes cook out the carbon buildup.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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