C;
When you "unplug" the line; can you feel/hear vacuum there?? You should and the engine should speed up when you re-connect it.
If it does not (speed up with vac) the vacuum advance can is bad and may be the cause.
Good luck.
PS: Your setting it right (line off-pluged) and you just slow the idle back down (speed screw) when the line's back on. Then smooth out with the mixture screw.
