In the earlier thread, you said:
"What I"m seeing is that the clutch side cylinder has gasoline POURING out of the petcock".
And in that same thread you said:
"...when it first started, the smoke was black. It did not contune smoling. Subsequent attempts showed white smoke- which I thought indicated it was too lean."
And in this thread a few days ago (21 Nov) you said:
"I am getting good fuel and the mist from the petcocks. The plugs do get wet though, so it might be flooding out".
All of those symptoms are typical of flooding, and may indicate you have a leaking needle valve, or that the needle valve seat isn't tight and gas is leaking past the seat gasket.
You've mentioned that you've "..rebuilt the carb, and have checked it about half a dozen times", but have you positively verified that the needle and seat are sealing properly? If they're leaking, this could be the source of your problem. And you can easily check this with a couple of different tests - one that F-I-T mentioned earlier was to loosen your carburetor from the manifold and hold it away with some small spacers such as wire rods or nails. If you have a leaking needle and seat, you will eventually see gasoline leaking out of that space held open by the spacers, and that leaking gasoline will run into your cylinders and will eventually fill up your crankcase. The other test is to use a float level test manometer that you can make yourself out of hardware store parts to verify your float level is correct and stays constant at the 3/4" level. If tractor is not running and the level creeps up something is wrong with your needle and seat or its gasket since gasoline is obviously leaking into the bowl when it shouldn't.