An internal combustion engine is running Lean when it has less fuel in the fuel/air mixture than it would have at the point of greatest stoichiometric efficiency. The penalties include premature detonation, which increases heat, reduces efficiency, and will damage your engine.

Running lean will also damage your spark plugs. Overheating will cause the electrode to be glazed, and the core "nose" (the ceramic piece around the core) will remain close to its original appearance. Detonation can cause the electrode and core to burn away, with the core nose having a burnt appearance. In more severe cases, it can even cause the core nose to chip or shatter. Any of these conditions will cause suboptimal sparking.

The antonym of lean (in this context) is rich.

Lean (?), v. t. [Icel. leyna; akin to G. laugnen to deny, AS. lgnian, also E. lie to speak falsely.]

To conceal.




© Webster 1913.

Lean (?), v. i. [imp. & p. p. Leaned (?), sometimes Leant (); p. pr. & vb. n. Leaning.] [OE. lenen, AS. hlinian, hleonian, v. i.; akin to OS. hlinon, D. leunen, OHG. hlin�xc7;n, lin�xc7;n, G. lehnen, L. inclinare, Gr. , L. clivus hill, slope. &root;40. Cf. Declivity, Climax, Incline, Ladder.]


To incline, deviate, or bend, from a vertical position; to be in a position thus inclining or deviating; as, she leaned out at the window; a leaning column.

"He leant forward."



To incline in opinion or desire; to conform in conduct; -- with to, toward, etc.

They delight rather to lean to their old customs. Spenser.


To rest or rely, for support, comfort, and the like; -- with on, upon, or against.

He leaned not on his fathers but himself. Tennyson.


© Webster 1913.

Lean, v. t. [From Lean, v. i. ; AS. hlnan, v. t., fr. hleonian, hlinian, v. i.]

To cause to lean; to incline; to support or rest.

Mrs. Browning.

His fainting limbs against an oak he leant. Dryden.


© Webster 1913.

Lean (?), a. [Compar. Leaner (?); superl. Leanest.] [OE. lene, AS. hlne; prob. akin to E. lean to incline. See Lean, v. i. ]


Wanting flesh; destitute of or deficient in fat; not plump; meager; thin; lank; as, a lean body; a lean cattle.


Wanting fullness, richness, sufficiency, or productiveness; deficient in quality or contents; slender; scant; barren; bare; mean; -- used literally and figuratively; as, the lean harvest; a lean purse; a lean discourse; lean wages.

"No lean wardrobe."


Their lean and fiashy songs. Milton.

What the land is, whether it be fat or lean. Num. xiii. 20.

Out of my lean and low ability I'll lend you something. Shak.

3. Typog.

Of a character which prevents the compositor from earning the usual wages; -- opposed to fat; as lean copy, matter, or type.

Syn. -- slender; spare; thin; meager; lank; skinny; gaunt.


© Webster 1913.

Lean (?), n.


That part of flesh which consist principally of muscle without the fat.

The fat was so white and the lean was so ruddy. Goldsmith.

2. Typog.

Unremunerative copy or work.


© Webster 1913.

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