GM-GMC: 92 GMC 3500, coolant temperature sensor, fuel pressure regulator

Question
5.7L V8 engine with carb fuel injection.the problem is that excess gas is causing so rich a mixture that it floods the engine. No codes to indicate problem. have replaced fuel pressure regulator. clouds of black smoke ans fouls plugs as fast as you can clean them.

Answer
There are only a couple of things that will cause a serverly rich mixture on those particular engines the most common one is the engine coolant temperature sensor (ECT)  If the ECT is not feeding the PCM the correct reading, the PCM cannot deliver the correct amount of fuel.  Generally when those sensors fail they cause an overfueling condition.  If you have access to a scanner, you can look at the engine data and the sensor will likely be reading something rediculous like -40deg when it is above 0 outside.  I would begin with replacing the sensor and see how it runs after.  You may need to replace the plugs also if they are fouled.
Hope this helps