1939 Farmall model A governor (not political kind)

Ordered all "A" tractor manuals from yesterdays but when the gov went on vacation the service manual says " see your service dealer"... Need help. Worked fine then just quit. There is a lock nut adjustable bolt on top of the body...what does this do? Any procedure for testing? Any help out there?
Greg

Not familiar with your specific application, but all governors work basically the same.

The governor arm connects directly to the carb throttle plate.

The speed selector arm on the dash connects to the governor arm with a spring.

Theory: The spring wants to pull the carb open, the governor wants to push it closed.

The lock nut is a stroke adjustment. With the engine off, and the governor spring removed, you should be able to move the governor to carb linkage freely from the idle stop screw to the wide open throttle position. If there is any binding, or the throttle won't close against the stop screw, or does not open freely, then the linkage may need adjusting or it is not in the right hole, bent, etc. Try every solution to external linkage adjustment before adjusting the jamb nut!

With the spring back on, and the speed lever in the idle position, engine off, you should be able to return the throttle to idle with minimal effort, or it may return under it's own power.

With the speed lever in the fast position, engine off, the throttle should be in wide open position. You should be able to return it to idle with moderate hand pressure against the linkage, with immediate spring back when released.

Now, with the speed lever at idle, start the engine. It should idle. Push the lever to high speed, the engine should rapidly rev to about 2500 RPM and level off.

If it over revs, the governor is bad or the spring is the wrong tension or adjusted wrong.

You can remove the spring and start the engine. It should idle. Then push the throttle open by hand. You should feel the governor push back, trying to return the engine to idle. If no push back, the governor is bad or the governor to carb linkage is still not right.

Don't be afraid to play around with it, it's nothing mysterious or complicated. Just be ready to cut the ignition in case of runaway!

What doesn't it do? When you move the throttle lever does it rev up? or just idle.
Could have a broken gov spring.

Backing it out will increase RPMS

That would be my guess also, based on the description of "worked fine, then just quit". I had the gov spring on my B break due to rust, and it was running fine then the next instant there was no gov control. I could still control the engine speed (roughly) by manipulating the throttle by hand, good enough to get me back to the house.