If the lawn mower engine produces black smoke , this indicates that the carburetor is getting too much fuel (or running rich). If the carburetor float is stuck open, the engine will get too much fuel. This is all fairly easy to do and is great DIY project to save some money on.
The fix is simple, check the mower for oil, and let the engine idle until the smoke clears. If your lawn mower is a tractor mower , white smoke usually means too much oil, carburettor fault, or blown head gasket. Charles, If your sears mower was equipped with the Briggs and Stratton eng.
If mower is still in good condition it would be well worth having diagnose especially if it was only needing head gasket or even simpler. This thing has been more trouble then its worth. It is starting to smoke while in use. In the olden days, you could get a lawnmower through the Sears Catalog, but now you ca. Thank you for the update but the smoke coming from the muffler is a white blue smoke or a black smoke.
Sometimes if breather goes bad it will saturate the paper air cleaner with oil and cause a black smoke as well as a white blue smoke. Blue or white smoke coming from your engine usually indicates burning oil, which can be caused by: Overfilling the crankcase with oil. You see the same phenomenon when you burn leaves and pack them too tightly to allow air to circulate.