John Deere 265 w FC540V being problematic

I have a John Deere 265 with and Kawasaki FC540V that I got in July of 2021. I rebuilt almost all the auxiliary components on the engine & it ran fine for a few months albeit with barely visible smoke.
In an effort to decrease the smoke I tried over and over again to tune it out trying many different methods and never got rid of the smoke. Then I decided to put the old carburetor back on because the new one was too far out of tune & the old one was still tuned. I put it on and sealed it & all that & also discovered that the smoke was caused by the throttle linkages being wrong, so the choke was always at least 1/3 of the way on. When all this was fixed, I started it up & it ran beautifully, the next day I started it & same thing. Then about 30 minutes later I went to park it in the barn, and it started beautifully but died when the governor went wonky. I tried to start it again and it would not start & would not start & would not start. Then it backfired so hard it sounded and felt like a grenade. At this point I am dead out of ideas. I tried a new carburetor, new spark plug, old carburetor, fixing the throttle linkages, timing the mag, & there is nothing left I can think of. Is there any expert out there that would have an idea what is wrong.

Had that engine on some golf course greens mowers and it started having problems about 2,000 hours and ran erraticly before stopping for good. It turned out be the plastic cam shaft gear had stripped off the teeth.