Handyman, I had a 520H and the way the book explained to move the tractor when it was not running was to pull up on the belt tensioner arm to loosen the drive belt and to move the motion control lever to the forward position. There was no other valve to open, so I would first think the drive belt or belt tensioning system to be worn and not operating properly. I liked the 520H it was a good tractor, I was just on it today at my son-in-laws ( I gave it to him ) I was pushing some dirt around. It brought back lots of memories.