Surging hydro?

[jimmystractor 171]

I have been messing around with a new to me 7119. This one seems to runs fine but the trans seems to surge. It is kind of hard to explain but basically I will have the hydro lever all the way forward and the tractor will be going along and then will slow way down and then pick up speed again. I'm not sure if there is an adjustment somewhere, the fluid needs changing or the hydro is going out...any help is appreciated!

[tadams 988]

What for shape is the drive belt ?

[yukon 331]

drive belt would be my guess to,plus lubricate all you joints.