Colt Case Ingersoll Garden Tractors

for diag. reasons .

Pull the fuel line off and block off it at the pump. Using a short hose and small augsilery fuel tank , give it a new fuel source and see if it changes or not .
If yes , you know something is wrong between the "tee" and the pump . If no then try adding propane gas down the carb and see if it helps or not.
You mentioned before that the PCV is plugged by someone prier to you . That makes me beleave that there is an intake leak to the crank case . If you block the fresh air side of the pcv it should richen up and not need so much choke . The intake gasket and or a flaw in the intake it self is bleading non metered air below the carb is what I suspect .
Have fun .

That leaking intake manifold is kinda my fear, but I'll hope for something less obnoxious. The carb cleaner all around the base of the carb didn't show any change, so I don't think it's just the carb base gasket...

If it's the intake manifold, it's just going to live like it is for the forseeable future. No way am I going to try to remove those bolts until I can park the whole unit for a while, because odds are good that will end up with the heads pulled due to broken bolts.