Small Engines (Lawn Mowers, etc.): B&S backfires when stopping, cub cadet lawn, adjustment screws

Question
I bought a BS ELS500 OHV 18.5 hp on a Cub Cadet lawn tractor Sept, 2004.  It ALWAYS backfires when I shut it down.  I've fiddled just a tiny bit with the carb adjustment screws but, other than changing the idle speed, nothing seems to change.  I purchased the machine at Lowe's so there is not much help available there.  Any hints you might give me will be greatly appreciated.

Answer
Hi Arnie,

The backfiring is caused by excess fuel going into the muffler, when the key is turned off and the engine is still pumping out unburned fuel.  This is normal and happens to all my engines.  To prevent it, let the engine idle for about a minute, then turn the key off.  This allows excess fuel to burn off.

Let me know how you make out.
Michael