GarageYears
I'm still not sure I can understand how/what the prop RPM setting can have over the behavior though - if the ADF ant. is causing some kind of RF shadow to fall over the VHF upper body antenna, how is RPM (above/below 2250RPM) factored into the equation? I presume some vibration effect?
It most likely has to be some vibration that cause whatever bit of metal that is the culprit to intermitantly connect/disconnect above a certain prop speed.
This mostly fits with the observation that the "onset" rpm rose slightly (but repeatabley) when the ignition was optimized which (probably) resulted in a smoother running engine.
Either that or the work somehow affected the culprit, access panel cycling or whatever.
Too bad we don't know if the engine off windmilling "onset" speed changed at the same time.
That would remove a smoother engined (and yet again the spark plugs
) from the suspect list