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went to look at the video and I got this instead. "This is a private video. If you have been sent this video, please make sure you accept the sender's friend request"
I have never heard of the balance effecting rpm's only that an out of balance prop. cause undue vibration. Maybe someone else will have more info....

I had my tach set incorrectly (me dumb). Now everything makes sense and original question doesn't apply.