Plugs are black
Well that ain't right; off the cuff there's a mixture problem.
I would start with screwing in the idle mixture all the way, then back out 1 1/2 turns, then adjust the mixture screw in or out 1/2 turn at a time to see if you can get a satisfactory idle. Starting with clean plugs is a good idea, that way you can monitor by colour of plugs if it's going pear shaped.
And I'm assuming you haven't been fiddling with anything else ?