What's the "rest of the story", has the tractor been in operation, and working correctly, or are you getting a neglected machine running again?
The governor spring acts to open the throttle, the weights act to counter the pull of the spring an hold the RPM's in check.
You say the weights move freely, are the little "fingers" on them that contact the thrust bearing intact?
Is the thrust bearing complete and intact (14)?
Next, the thrust bearing contacts the "fingers" on the governor fork (13). Are they intact?
Is governor-to-carburetor rod length adjustment correct?