Lycoming O-235 series, Operator'S Manual

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LYCOMING OPERATOR’S MANUAL SECTION 3
O-235 AND O-290 SERIES OPERATING INSTRUCTIONS
6. CHECKS BEFORE TAKE-OFF.
a. Warm up as directed above.
b. Check both oil temperature and oil pressure.
c. Set carburetor air heat control for “full heat” to check operation. Loss of manifold pressure or RPM
(or both), depending on whether a fixed pitch or controllable pith propeller is installed on the aircraft,
will result if the control is working properly. Return control to “cold” position after check.
d. A proper magneto check is important. Additional factors, other than the ignition system, affect
magneto drop-off. They are load-power output, propeller pitch and mixture strength. The important
thing is that the engine runs smoothly because drop-off is affected by the variables listed above. Make
the magneto check in accordance with the following procedures.
(1) Controllable Pitch Propeller – With the propeller in minimum pitch angle, set the engine to
produce 50 to 65% power as indicated by the manifold pressure gage. Mixture control should be in
the full rich position. At these settings the ignition system and spark plugs must work harder
because of the greater pressure within the cylinders. Under these conditions, ignition problems, if
they exist, will occur. Magneto checks at low power settings will only indicate fuel-air distribution
quality.
NOTE
Aircraft that are equipped with fixed pitch propeller, or not equipped with manifold pressure
gage, may check magneto drop-off with engine operating at approximately 1800 RPM (2000
RPM maximum).
(2) Switch from both magnetos to one and note drop-off, return to both until engine regains speed and
switch to the other magneto and note drop-off, then return to both. Drop-off should not exceed 175
RPM and should not exceed 50 RPM difference between magnetos. A smooth drop-off past
normal is usually a sign of a too lean or too rich mixture.
(3) Do not operate on a single magneto for too long a period, 2 to 3 seconds is usually sufficient to
check drop-off and will minimize plug fouling.
7. OPERATION IN FLIGHT.
A. See airframe manufacturer’s instructions for correct manifold pressure for power settings.
B. Fuel Mixture Leaning Procedure – Improper fuel-air mixture during flight is responsible for many
engine problems, particularly during take-off and climb power settings. The procedures described in
this manual provide proper fuel-air mixture when leaning Lycoming engines. They have proven to be
both economical and practical by eliminating excessive fuel consumption and reducing damaged parts
replacement. It is therefore recommended that operators of all Lycoming aircraft power plants utilize
the instructions in this publication any time the fuel-air mixture is adjusted during flight.
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