Small Engines (Lawn Mowers, etc.): Lawn Mower, adjustment screws, engine speed

Question
 My B&S Classic engine runs sluggish and the spark plug gets covered with soot.There are no adjustments for increasing air flow or increasing engine speed (outside of the mule and rabbit throttle handle ).The owners manual advises not to attempt changing the factory set controls.
How do I make the engine run clean and vary the speed control?
 Many thanks.Jerry P.

Answer
Hi Jerry,

First check the air filter.
Then, double check for mixture adjustment screws on the engine. If you find one, try screwing it in 1/8 turn at a time.  Next, you could remove the carb, disassemble it, clean all the small openings and add a rebuild kit.  As a last resort you could try a hotter spark plug.

Let me know how you make out.
Michael