Small Engines (Lawn Mowers, etc.): rough idle/run with black smoke, fuel mixture, push mower

Question
I have a Troy-built Series 540 Push mower that is about 1 year old.  It is now running rough with a rough idle and some black smoke.  I am planning an oil change, should I be looking into checking anything else.  I have little to no knowledge about small engines but can manage basic tasks

Answer
From what your telling me I would assume your in need of a carburetor rebuild, seems it is running too rich (too much fuel). Only other reason could be  the choke not fully opening. If the choke plate is fully open when the engine is warm after a few seconds, then it is in need of a carburetor rebuild. I am also assuming you have a clean air filter, if the air filter is dirty it will not get enough air and will be receiving the wrong fuel mixture. A carb rebuild is best left to the local shop.Keep me updated.... Tom