While flying around the local area my friend in the front seat of my Cub pointed at the taco/rpm guage, which had sprung from 2100 up to 3600.
She said "that doesn't seem right?!" (while pointing furiously at the thing - she's a pilot too!)... I said "no, it isn't. But that's a lovely view and down there and I reckon that pub would be a great place for lunch". After an hour or so we landed.... Happy days.
Few weeks later we changed the taco drive cable.