Mecanim curve for move speed

We have a blend tree in Mecanim that has two motions, Walk and Run. Can we use Mecanim curves to control the move speed of the character?

We tried putting a curve in the run animation that goes from 0 to 6 with both controls points set to Clamp. However this way, when the character moves his speed just loops between 0 and 6 when he is running.

I would have thought that if the curve's control points are set to Clamp then the speed would remain whatever it was at the endpoint of the curve instead of looping back from the beginning of the curve.