Because I'm too damned dumb to pound sand.
The problem the Director reported fit the symptomology of bad fuel/dirty filter. Went thru the cursing/sweating/bleeding evolution, and the BX crunk and ran right well. With the Director in the seat (weighing in at about .4 of what I do) she put the HSD in low, and it sounded as if she had turned off the engine. Got down to about stall RPM, kicked it back to neutral, and it roared back to life. Turned it off, I hopped on it, crunk it, and got it to stagger back into the barn.
Further research suggested that the deadman switch that detects weight on the seat was failing. Replaced that bit, and the li'l tractor runs the best it ever has.