OK, this is serious. We have had a number of overspeeds on our R44s where the symptoms were exactly as you describe. In fact we are investigating several of these and we think that it may be down to the quality of the signal from the points in the left magneto going to the Governor Control Box.
I suggest that you get your magnetos changed and please put in an MOR. This could become a major problem if we as customers don't get Robinson to first of all recognise that there is an issue and secondly do something about it.
We are currently in discussion with RHC but we need a lot more ammunition.
Please pm with details and a copy of your MOR.
Thanks for your help.