Biohazard
Got inside the carb's bowls and lifted out the floats. Looks like some black gunk had formed on the bottom of the floats and there was a matching pattern at the bottom of the bowls. Suggests that the gunk had sort of glued the floats to the bottom, keeping them from rising and closing off the inlet valve. At least I hope it's that easy. However, while removing said floats, the hinge pin fell out and promptly scurried down that U shaped opening between the number 3 and 5 cylinders never to be seen again. I can order one for $11 but found that some 2" finishing nails I had were the right diameter so I'm going to carefully cut one down to 3/4 of an inch and pat myself on the back for having done so.