I'm not sure about the vacuum advance, but as far as your idle goes mine did the same thing. Finally figured out that it was the idle cut solenoid(sp). I just cut the wires to it and left it in the carb, gets a little worse gas mileage but it runs. Really easy to find too, follow the wires going to the carb, there should be 4 of them, 2 go to the choke and the other 2 go to the idle cut solenoid(sp), I was told by a carb shop that if you just cut it, it won't mess anything else up, just knock the mpgs down a little.....you do need to leave it in there however, to plug the hole. If you're a little better in the $$$ department then me then just replace the thing, but I'd try this before I started buying parts.

Good luck!