Small Engines (Lawn Mowers, etc.): BACKFIRES, gas vapors, head gasket

Question
12.0 HORSE POWER BRIGGS AND STRATON ENGINE.BACKFIRES WHEN TURNING OFF IGNITION..I CLEANED THE CARBURATOR CHANGED THE SPARK PLUG BUT IT STILL DOES IT.

Answer
 Hello Serafin:

 Lean the High Fuel Mixture a Little until the Backfiring Stops. If you Start to Lose Power Stop. Enrichen the Fuel Mix 1/4 Turn. This Means the Muffler is Filling Up with Unburnt Gas Vapors. Allow the Engine to Run at Idle for a Couple of Minutes to Cool Down. Then Turn Odd the Engine. The Exhaust valve May Not be Seating Properly or Depending on the Model of this Engine a Bad Head Gasket Between the Cylinder and the Valves will Cause this to happen. If your Engine can Accomadate the Cigar Style Muffler, this Sometimes Helps. One of those Should Cure the Problem. This is a Common Characteristic of Some Engines Built Today. I have seen this Many Times and Usually a Couple of Cool Down Times Works the Best if the Head Gasket and Valves are Good. Hope this Helps. Let me know what Happens, Please.

 Good Luck

 Respectfully

 John