1. With the engine stopped move the throttle linkage back and forth in pic 1. If it has full travel the throttle shaft and governor are not frozen.
2. Move the governor arms back and forth to check free travel, no binding or wobble. Pic 2.
3. The control rod linkage guide is the most likely place for binding and seizing up. Pic 3.
4. There are 3 springs in the throttle control linkage. All springs tension to close the throttle. Parts schematic Pic 4.
4a. Governor spring. Pic 2.
4b.Throttle rod return spring and hand throttle return spring Pic 5.
4c. Another view of hand throttle return spring. Pic 6.