Flying Kiwi
Further to BackPacker above, I quote from Lycoming literature, for float-type carburettor (for best economy) lean to roughness, then enrich to smooth running. Lycoming do not foresee an advantage in fitting an EGT over this method. The problem is fuel distribution over all cylinders. If you have an EGT then lean for peak EGT. However, if this results in rough operation of the engine, then still enrich for smooth engine operation = no advantage in fitting EGT.
Do not try “Lean-of-Peak” with these simple engines. Charles Lindbergh had big radial engines.
For a more sophisticated engine set up (injectors, individual EGT’s, GAMI’s) “Lean-of-Peak” is probably permitted and in deed the recommended cruise setting. One would normally refer to the Flight Manual, however in my experience many Flight Manuals do not adequately cover this subject.
While on the subject also investigate if “over-square” engine settings are appropriate. Also a legacy from radial engine operations.
I once knew a pilot who insisted full rich was better for the engine as it operated cooler (no evidence to support this) and would not be told otherwise. Utter rubbish, waste of fuel and risk of plug fouling. This pilot made a long over-water flight to an island and managed to run out of fuel 10 miles short resulting in a water ditching and loss of aircraft. I’ve long held the opinion that if the pilot had aggressively leaned, the outcome would have been successful.
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