Leaning Precautions; Leaning To Exhaust Gas Temperature Gage; Leaning With Manual Mixture Control; Alternate Method - Lycoming O-290 Operator's Manual

SECTION 3
OPERATING INSTRUCTIONS
Never exceed the maximum red line cylinder head temperature limit.
For continuous operation cylinder head temperatures should be maintained below 435°F (224°C).
On direct drive engines with manual mixture control, maintain mixture control in "Full Rich" position for
rated take-off, rated maximum continuous, climb and cruise powers above 75%. However, during take-off
from high elevation airport or during climb, roughness or loss of power may result from over richness. In
such a case adjust mixture control only enough to obtain smooth operation – not for economy. Observe
instruments for temperature rise. Rough operation due to over rich fuel-air mixture is most likely to be
encountered at altitude above 5,000 feet.
Always enrich mixture before increasing power.
C. LEANING TO EXHAUST GAS TEMPERATURE GAGE.
(1) Above 75% power – Never lean beyond 150°F on rich side of peak EGT unless aircraft operator's
manual shows otherwise. Monitor cylinder head temperature.
(2) 75% power and below – Operate at peak EGT.
D. LEANING WITH MANUAL MIXTURE CONTROL. (At 75% power or less without flowmeter or EGT
gage.)
(1) Slowly move mixture control from "Full Rich" position toward lean position.
(2) Continue leaning until engine roughness is noted.
(3) Enrich until engine runs smoothly and power is regained.
E. ALTERNATE METHOD. (In calm air and engines with fixed pitch propellers.)
(1) Slowly move mixture control toward lean position while closely watching tachometer. Continue
leaning until RPM decreases.
(2) At this point enrich until RPM just peaks. Correct fuel-air ratio is obtained at this point.
Leaning may be done at any altitude that the engine will accept leaning: The greater the
altitude the more important leaning becomes. Proper leaning is important because more
engine power and increased air speed are obtained along with decreased fuel consumption,
longer spark plug life, less lead fouling, and more normal oil and cylinder head
temperatures. Engine damage from leaning the mixture does not occur at the specified cruise
power for the model engine in a basically healthy power plant, but is the result of improper
leaning at power settings above recommended cruise.
3-4

LEANING PRECAUTIONS

NOTE
LYCOMING OPERATOR'S MANUAL
O-235 AND O-290 SERIES