I stand corrected. Should have gotten my facts together more. Its good Y'all are keeping me honest.
Found an article that might help explain why a lean fuel/ air ratio isn't good for an engine.
http://en.wikipedia.org/wiki/Air–fuel_ratio_meter
Lean mixtures improve the
fuel economy but also cause sharp rises in the amount of
nitrogen oxides (NOX). If the mixture becomes too lean, the engine may fail to ignite, causing misfire and a large increase in unburned
hydrocarbon (HC) emissions.
Lean mixtures burn hotter and
may cause rough idle, hard starting and stalling, and can even damage the catalytic converter, or burn valves in the engine. The risk of spark knock/
engine knocking (detonation) is also increased when the engine is under load.
Google is my friend...