Two more things to look at... Turn the idle speed screw clockwise to bring the idle up to a point it will stay running. Then turn the idle MIX screw either way and look for an increase in speed. As it increases turn down the idle speed screw to compensate. Keep doing this until the MIX screw stops having an effect or actually decreases the speed. When it decreases the rpm go back to the highest point, and 1/4 turn beyond that. That should set you straight
I should have said to check this first. The auto choke... Remove the 2 little screws that hold the retainer in, and pull out the choke as a unit. You will see a tiny "O" ring where it goes into the carb body. Don't damage it.
Now turn on the Ign key, and carefully watch the brass pin. It should move outward very slowly to an extension of about 4mm. That tells you it is working. Let it cool w/ the key off for a few minuets, and reinstall it if it is good. Careful of the O ring.
If it does NOT move during the test put a meter or test light on the two wires, and you will see 12v with the key on. If not track down the issue.