You might have a belt that isn't uniform in either width between the two v's or the individual ve's are not made right and it is climbing and going down in their each groove . I would try a different belt and I think that you tighten the adjuster up to where the sleeve touches and then a bit more to help take the whip out . Most of the whip comes from the engine each time it fires especially at idle .

 

First of all, you don't need to pull hydro to replace belt. Reach up in there and unbolt the pulley and slide towards hydro pump. That should give enough room to slip belt in/out. For the belt jumping, I have come across an issue in the past where the new belt was too long and would rub in the middle where the tensioner pulley held the top and bottom parts of belt close together which would cause the belt to jump bad. Found the correct belt and never had trouble since.

 

Make sure the tensioner pully is dead on straight and the washer on the spring contacts the tube and just like the comment from schaaftr don't take the hydro off, no need for that!

 

Well.....Got the belt off and measured the thickness of it with some calipers. I have a total difference of .050 in thickness. Prolly not enough to make it jump like that,and i really have no good way of measuring the groove down the center as marshall suggested. I took the tensioner pulley and bracket off and when i spin that pulley the bearing sounds a little rough. will spin forever like its free but am going to replace it and the belt as well. The replacement rods ih sells these days are chincy compared to the original one that was in there. I'm gonna chase some threads on a good piece of steel that is truly 1/2 inch in diameter and use that. The weaker those rods are the more chance for flexing. I'll get my parts here soon and report back with results. Thanks for the all the suggestions.

 

New belt,new tensioner pulley and bigger,stronger tension rod. Runs nice and smooth now. Thanks for the help guys.