Hello

Got a XT660X 2004 engine I had removed from a damage frame to a good one and going to registrate the new one. Started the engine before I took it from the damage frame to see everything is ok. Now after I mounted it in to the good frame and started it the speedo flips out. When it is on idle the display shows for example 6km/h. When I rev up the engine it the km/h increases.
What could be wrong?

Thanks!