Hi Jeff,
It looks to me like your tail blades are spinning backwards.
It is hard to tell from the video, but the front half of the tail rotor, the half closest to the main blades, should be traveling up.
The second vid does not show it, but the first does at 45 seconds, and a little more clearly at 1:03.
Again, I am not positive that it is backwards, it could just be a trick of the frame rate of your video camera.
Try turning the main blades by hand, in the proper direction of rotation. The tail blades should rotate up through the downwash of the main blades.
If they do not, then it means that your twist in the belt went the wrong way.

Let us know if this in indeed the fix.
Vince