Originally Posted by
Mark1234
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There's no reason that the thing should shake with one mag off either, on the occasion of an engine developing a somewhat unpleasant vibration after meeting a rain shower, I finished up completing the flight on just the right mag because it was misfiring and shaking when the left was on - there's two for a reason.
Consider also that I'm pretty sure your static RPM will be affected by density altitude (but so will the power output of the engine, so I'm not too sure of the exact relationship..)
I had a similar case, although in this incident there wa an internal failure of one mag which greatly advanced the timing for the firing of the spark plugs of that mag. The engine all of a sudden started running very roughly. Swiching off the affected Mag returned normal engine operation and an uneventfull landing at the nearest airport (fortunately home base) was carried out.
With regards to the second point. The relationship between engine power and density altitude vs static RPM is not exact but close enough that for practical purposes the static RPM will not vary appreciably, unless you are at extremes of temperture and altitudes.