Easy. Lift the fuel cut-off solenoid plunger (called the governor solenoid in the TM but isn't directly controlling the governor). Watch the lever with the ball link stud to see if it moves up freely. With solenoid in the full up position, attempt to rotate this fuel control lever, it should move freely with just minor spring force. You can also try disconnecting the ball link and remove spring force issues.
This lever directly controls injection quantity, the only engine speed/torque control. And because its position is controlled by the very minor governor-spring forces (spring when RPM is low, governor when RPM is high), any resistance to movement will result in RPM issues.
Now, if this lever doesn't move freely, Berryman B12 Chemtool will dissolve diesel varnish. It also peels paint so watch out! You may need to use some inside the injection pump but do not soak for extended periods as it swells O-rings. B12 also doesn't lubricate the injection pump so don't run the engine until the pump is flushed with diesel. The priming pumps and clean diesel in the set tank will do just that. NEVER use tools to free up the control lever, just fingers.
If the chemical method doesn't work, don't despair, the control lever CAN be removed without pulling the pump. But it is difficult and requires small fingers, a dental mirror and grease. Remove the ball linkage, solenoid and starter cut-out cover for room. Then cut the fuel limit wire and pull the stop screw, counting the turns (or measuring). Now bend the two screw tabs flat and remove the screws. The control lever can now be pulled and soaked/cleaned. There is one small part, the pawl. It fits into the control shaft on an eccentric hole. A dab of grease in the hole will retain/fix it for reassembly.
Reassembly is the tricky part. Grease the new o-ring and pawl. Note the slot in the control collar (inside the IP,), this is what the blade of the pawl engages, moving the collar sideways (as installed). The blade of the pawl must be vertical AND the shaft rotated to align the pawl. It will only seat fully when engaged AND the lever must freely turn until hitting the engine block or stop bracket. It will take you several attempts, it can be done even in the field. Just good lighting and a clean mirror.
Once fully seated, install screws and bend tabs to secure. Then reinstall the max fuel stop screw, counting the turns. This is only the smoke limit, if the engine emits black smoke under sudden load, screw it in a half turn until smoking is stopped.
The governor adjustments are in the -34 TM, you shouldn't need to adjust these as the control lever cleaning procedure doesn't adjust these.
