IO-240 Series Engine Installation & Operation Manual
4-11
31 October 2011
Engine Operation
WARNING
Absence of RPM drop during the magneto check may be an
indication of a faulty ignition circuit resulting in a condition
known as “Hot Magneto.” Should the propeller be turned by
hand, the engine may inadvertently start and cause personal
injury or death. This condition must be corrected prior to
continued aircraft operation.
CAUTION: Do not underestimate the importance of the magneto
check. When operating on single ignition, some RPM drop should be
noted. Normal indications are 25-75 RPM drop and slight engine
roughness as each magneto is switched off. RPM drop exceeding 150
RPM may indicate a faulty magneto or fouled spark plugs.
NOTE: If the engine runs roughly after single magneto operation,
increase engine speed to 2200 RPM in the BOTH position and lean the
mixture control until the RPM peaks for ten seconds before returning to
the full rich position to clear the spark plugs and smooth operation before
returning to single magneto operation.
Limit ground operation to time necessary to complete engine warm-up and pre-flight
checkout.
7. Throttle.............................................................. 1700 RPM
a. Magneto Checkout
1) Ignition Switch ...................................... R
RESULT: Noticeable RPM (not to exceed 150 RPM) drop and slight engine
roughness; record Left Magneto channel drop results. Maximum allowable
RPM drop spread between magneto channels is 50 RPM.
2) Ignition Switch ...................................... BOTH
RESULT: Engine speed returns to normal. Allow Ignition switch to remain in
BOTH for approximately 30 seconds to clear engine.
3) Ignition Switch ...................................... L
RESULT: Noticeable RPM (not to exceed 150 RPM) drop and slight engine
roughness. The difference between magnetos individual operation should not
exceed 75 RPM. Maximum RPM drop for either magneto is 150 RPM.
Observe engine smoothness during magneto switching.
CAUTION: Do not operate the engine at speeds in excess of 2000
RPM longer than necessary to complete ground checks. Proper
engine cooling depends upon forward motion of aircraft.
Discontinue testing if temperature or pressure limits are
approached.
b. Minor spark plug fowling can be cleared as follows:
1) Ignition Switch ...................................... BOTH
2) Throttle.................................................. 2200 RPM
Summary of Contents for IO-240-A
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