One thing that i noticed was a lot of cars in warm weather climates just run water in the rad and most will get rust/corrosion build up in the motor that leads to over heating ...do a good cooling system flush and change your thermostat ...black smoke when you first step on it is fuel before your boost builds ...i'd get a boost gauge to make sure you are making proper boost (10-12psi) ...i'm running 25+ PSI boost with my fuel turned up 1 1/2 turns and i still get black smoke ....and LOTS of power

'87 Raider 4D56 ...lots of boost
'86 Toy xtra cab 2L-T
'82 Benz G Wagen 300GTD
'82 VW Caddy TD
'79 LJ81 Zuk p'up 1.6TD