M20E A3B6D run up

[N3417X]

I've recently noticed that my m20e, with the A3B6D engine upgrade, isn't dropping on the left mag; however, the right mag drops within limits and it will shutoff with the ignition. Would this be an ignition issue?

Dennis

[MooneyBob]

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[Andy95W]

Sounds like you have a hot right mag.

When you move the switch to Left, the right magneto should be grounded so the engine is only running on the left magneto. Since yours doesn't drop RPM, it means that the engine is still running on both.

Either your P-lead is broken, disconnected, or your switch is malfunctioning.

[carusoam]

If you have a JPI or other engine monitor...

You may/should notice a rise in EGT when running on one magneto vs both.

If you really lean the mixture, it may make it difficult to notice the drop in RPM.

Either way, the rpm drop is normal. Not having an rpm drop needs further attention.

Get familiar with the P-lead on each magneto. See if one is broken or disconnected.

Best regards,

-a-

[MB65E]

Check to see if the key kills the engine in the off position. If it does turn the engine off its in the switch itself. That darn switch labeling always bends my brain cells. I wrote it down once... Lol.

Sounds like one hot mag.

-Matt

[Jerry 5TJ]

...my m20e, with the A3B6D engine upgrade, isn't dropping on the left mag; however, the right mag drops within limits and it will shutoff with the ignition....

Since the key will kill the engine both mags must be grounded successfully by the switch and harness.  That suggests the switch has failed in the L position but works OK in OFF, BOTH and R positions.