black smoke, floating valves

[2.4niz]

I have a 1992 240sx with the KA24DE, under heavy acceleration, sometimes not necessarily heavy, I get black smoke out the exhaust, which means the mix is rich. I have heard the ka has problems with injectors leaking. When I bought the car someone had done a compression check, it was between 170-175 for all 4 cylinders, but I haven't done it myself yet. Blue smoke would be rings, or oil getting past the valve guides, I'm just wondering what I should try before getting new injectors.

I guess the valves tapping at idle probably doesn't help... but if I raise the idle about 100 rpm, it goes away. Anyway, any advice on the black smoke would be greatly appreciated