When cold the tack does not read at idle, when revved it shows roughly twice of what is actual. After a couple of minutes running it slowly begins to read right.
Any thoughts on what the problem might be? Common to Ducs?
There are a couple threads on this. If you put light finger pressure on the face of the tach when it is acting up and it goes back to normal, then this most likely indicates the brass screws on the back side of the tach need a bit of torque.
The screws are supposedly responsible for the internal electrical connection.
It takes a bit of work to get the tach out, but iot is an easy fix.