"Lean of peak engine operation – is it good or bad?" - Reno
“Leaning beyond peak requires balanced injectors and a graphic engine monitor to be used successfully. Carbureted engines are less likely to run smoothly lean of peak, due to uneven fuel distribution.
Lean beyond peak is a good way to save fuel, that’s a plus. A minus of this approach is that improper management of the mixture could lead to expensive engine repairs because of overheating and potential detonation. Be sure to understand the proper technique for your aircraft or you could have a bad result.
In addition, running lean of peak will reduce power slightly and therefore will result in less than maximum cruising speed, which could be bad depending on your priorities and expectations.
Know and understand how to properly operate your airplane and compute performance figures.”