Honda HRM215 governor problem

I was given a Honda HRM215 lawn mower with a GXV140 engine by a friend because he no longer mows his own lawn. The mower had been sitting in his garage for a few years and he did not drain the gas after he last used it. When I got it, it would not start. After I cleaned out the carburetor I was able to start it. But it never ran right and would stall after running for 5-10 minutes. It looked like the engine was running too slow and I tried adjusting the throttle screw to no avail. I found some video on youtube about adjusting the governor to make the engine runs faster and decided to give it a try. When I tried to turn the governor arm shaft after loosen the bolt, it was so tight that I could hardly move it in either direction. After I tightened the bolt and restarted the engine, it was running so fast that it actually back fired a couple times and I could smell the unburned gas. The governor arm did not move and was always in the full throttle position. When I pushed the arm toward the carburetor, the engine slowed down. Looks like I might have messed up the governor inside the engine that it no longer controls the shaft. One thing I notice is that I can move the shaft and the arm in-and-out for about an inch which I think maybe the shaft is disconnected from some mechanism internally. I tried adjusting the governor arm shaft a few more times and could not get the engine to slow down. I am running out of ideas and any help is appreciated.

Honda HRM215 governor problem