Yeah, when I said we 'got somebody to poke at it', I mean he did take the carb off and clean it out. The needle was stuck. He also pulled the gas tank off and cleaned it and put a new sediment bowl on it.
But it looks like he re-used the old gasket between the carb and intake manifold, and any other gasket he'd have just sat down with an exacto knife and cut out to make a seal. But there's a loud hissing sound from that area of the tractor. (I did notice that some hissing was heard out the dipstick hole, but I think this may be something else.)
Anyway I did a (very) crude test and wrapped duct tape around that gasket and I did get smoother acceleration through the lower third throttle range--that's why I think that should be replaced.