Dan Hauter wrote: The tractor started but ran rough and smoked. ... If I found the right spot on the choke the tractor would run. I kept adjusting the needle valve & finally got the tractor to run at idle but I couldn't throttle up.

Okay, so some things don't add up here.  If it's rough and smoking, but you can pull out the choke to make it run... and it'll idle but not throttle up...

In the realm of a fuel system problem, these don't equate.  If it's running rough and smoking, that means you're not getting incomplete burn cycle, so it's over-rich... which in a fueling context means you either have an obstructed intake, too high a float level, a failed/stuck float valve, or an obstructed exhaust...

But pulling out the choke obstructs the intake, thus forcing an enrichment, which would NOT lean out an over-rich condition, it would simply make it worse, not better.

The fact that it won't throttle up is another oddity.

Put them all together, and I'm gonna bet that this is actually an ignition problem.  You could have a stuck advance mechanism, a sacked-out contact point spring, or the points and/or point cam is worn, or the distributor shaft bushing is worn out and sloppy, or the condenser is bad... or the coil has failed...  or any combinations of any-or-all-of-the-above.

If it's not that, pull of the manifold and check it for obstructions (a mud-dauber nest in there... or a crack between the exhaust side, and the intake side, thus leaking exhaust into the intake).

If that's a Carb that I rebuilt, the reason the enrichment needle is left out is for shipping purposes. Just taking precautions so the "candycane" enrichment needle doesn't get damaged. There are instructions on how to adjust the enrichment and idle circuits and where I put them for a starting point. The venturi being left out is highly unlikely, but hey, I'm human too. But doubtful. Sometimes in shipment the pkg gets banged around and maybe the floats are stuck. I address that in the instructions as well. Also, the other problem that happens with newly rebuilt Carburetors is opening up the petcock to fast. Incoming fuel push the floats up quickly and fuel bowls overfill. Usually the first indication of that is fuel running out the intake or intake vent in the floor of the intake bore of the Carburetor. If you don't have that, it's not overfueling. If Black smoke is coming out of the stack, that's an enrichment problem which you can easily take care of with adjusting the enrichment needle at WOT. If the engine won't rev up, there's another problem somewhere hindering the engine. Check timing, spark plug firing order, old fuel, points, bad condenser somethin' there is not right. You'll figure it out.....

Steve@B&B