Sporadic Engine Surging

[wpollock]

I have a 6hp Briggs, model 12H802-1776 Type B-1, on a Toro GTS Recycler mower which I have posted about in this forum before and have received generous and informative answers. This engine is self-governed and engine speed varies little even under a heavier cutting load. It has, for the most part, run consistently at the same rpms until yesterday when it started to act as if the engine is losing fuel supply even though it has a full tank. It belches a puff of black smoke every once in a while and has yet to die when running. I have used it for 4 full mowing seasons having only rebuilt the carb the year I got it. Could my issue possibly be related to it needing a new spark plug?
Thanks for the thoughts.

 

[Born2Mow]

Black smoke is excessive fuel. Remove the top engine cowling and remove all the grass clippings from the top of the engine and in/around the carb actuating rods. Don't do this with water, high pressure air is highly preferred.