Mark if it runs better with a little choke, that is the classic plugged idle jet in a Carter carb (assuming no vacuum leaks). The Idle "Jet" is actually a tube with a tiny and I mean tiny hole in it. They plug up for any reason they want. I have had and still see, the tube jet plugged brand new. The natural corrosion of the brass produces a very small nearly invisible green crust. It plugs that tube right up brand new. Anything in the fuel system will plug it if it finds its way there. When they are severely plugged the engine will not idle without the choke helping. I use a tiny wire and clean it out with that. When you hold it up to a light you will see why they can cause trouble. The hole is so small you have to hold it just right to see any light through it. The slightest piece of crud and, its plugged. If the idle air adjustment does very little to the idle, the idle fuel circuit is suspect. It sounds like yours is approaching wont even idle. Take a look at a drawing on what that jet looks like. It is a tiny "crap funnel".