Michigan 55a

I have an old Michigan loader with the 3-53 Detroit. It runs good, everything works like it should for a fifty year old machine, but I can't keep it ideling. I've adjusted the valves and what not according to the service manual but the idle speed screw doesn't seem to do anything. I've screwed it all the way in and out with the engine running but nothing changes. The engine runs smooth, there doesn't seem to be anything else wrong other then idle speed, so I'm guessing it's governor related....

Michigan 55a

Michigan 55a