I did some more testing - I have a friend's 2.10 here for minor repairs. It runs well, so I did some experiments with his carb and my bad one. Note that a very careful inspection of my carb shows absolutely no dirt, gum, etc. in any passageway.
With his good carb, the HS needle will completely shut off the incoming fuel. With my bad one, it still allows (large amounts) of air to enter, even when closed. His NV and even a BRAND NEW one made no difference. Maybe the spraybar opening is worn to the point that the NV won't seal it off? This could explain fuel gushing out the carb when the plane is on its nose, as noted in a previous post.

This almost makes it seem like the engine is flooded! That would explain the fact that I can’t get it to pop once it quits.

Jim