Slant six idles rough

No vacuums leaks. Has good power. Just at idle it runs a little rough. It gets better as it warms up but once warm it still shakes some. It’s pretty bad when it’s cold and will spit some black smoke before the choke opens up but once open all the way, still a little rough
And you know this how? Have you put a vacuum gauge on it? Try partially closing the choke when it's idling rough and see if that cleans it up.