It really sounds like the low end is not set right. I'm assuming it's an "air bleed" type carb, which means the low end needle adjusts the amount of air the carb gets (rather than fuel). If this is the case then turning the low end needle clockwise will richen the mixture, counter-clockwise will lean it.

First thing I'd do is try adjusting that low end. If that doesn't work, then I'd say something truly is wrong with the engine.

Sure wish I could actually get my fingers on that thing for a few minutes.
Dennis-