Good news: I got my 2165 running smooth again. Turns out, I was the cause of the problem:
Last winter, I replaced the starter motor on the engine. While I had half the engine torn down to get to one starter bolt, I noticed the metal tube on the back of the carbuerator didn't have a hose or a rubber cap on it. I put a rubber cap on it. I assumed it was a vacuum port, because it looks like one. It wasn't.
It's a breather tube for the carb float bowl. By having it plugged, it must have created a positive atmosphere inside the bowl, and probably forcing the needle to stay open, thus dumping too much fuel into the engine. (or something like that).
Either way, as soon as I removed the plug, it ran like a champ.
In troubleshooting this, I had started by having the engine running. I removed the air cleaner assembly (5 bolts). As soon as I did that, the engine ran better. I had scratched my head for a bit on that. I then re-installed just the bolts without the air cleaner, back into the carb. As soon as I did that, it ran crappy again. Aha! Peering down into one of the bolt holes in the carb, I could actually see gas in the float bowl. (I figure when they drilled the bolt holes originally, they went all the way through to the bowl area.)
That got me thinking about it needing atmospheric air to function properly. Then the light bulb came on, as I was staring at the rubber cap I had put on the carb months before. Problem solved. And I won't have to buy a new tractor now - yaaa !