Thanks for clearing that up. Now I know what kind of hole to look for. Maybe it's even clogged (engine is old) and thus could be why we couldn't get the low end leaned out.

Plane was slobbery rich at idle, so much that fuel was splashing out of the carb and engine wouldn't idle lower than 1/3->1/2 throttle.

So how does the throttle stop screw work?

Unfortunately the 46LA manual has pretty lousy instructions for the carburetor, other than the standard OS instructions for tuning the high end.