Dax Cobra Speedo problem

[anonymous-user]

so out on a drive today and all going fine, until suddenly my speedo started showing approximately double the speed I was actually travelling at (unless 140 mph really is that quiet!)

Any clues as to what might be causing it and how to fix it?

I'm assuming its an electronic speedo (I didn't build the car) as I can't see any way a cable driven speedo could do that

TIA