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Lycoming YIO390A3B6

design4p

Active Member
Here in the UK and completing my Light Aircraft Association application form for a permit to test fly having just completed my RV14A build.

Just wondering what the standard Magneto test settings are:

Test RPM
Max RPM Drop permitted
Max RPM Split permitted
Alternative Air test RPM

Regards John
 
This is a cut and paste from section three of the Lycoming Operation Reference Manual. I've also attached a link to the manual below. Theres a warning on the first page that this is for a basic IO390, may not be applicable to all models, etc.etc.

(1)
Fixed Wing Aircraft.
(Controllable pitch propeller.) With propeller in minimum pitch angle, set the engine to produce 50-65% power as indicated by manifold pressure gage. 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.
(Fixed pitch propeller.) Aircraft that are equipped with fixed pitch propellers, or not equipped with manifold pressure gauge, may check magneto drop-off with engine operating at approximately 1800 RPM (2000 RPM maximum).
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. Magneto drop-off at 2000 RPM should not exceed 200 RPM on either magneto; but under some conditions; i.e., field elevations and temperature characteristics, a drop in excess of 200 RPM (plus 25 RPM) may be experienced. If engine speed stabilizes and if the engine continues to operate smoothly, the ignition system is operating satisfactorily.

Here's a link to the entire document:

https://www.lycoming.com/sites/default/files/60297-29.pdf
 
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