Small Engines (Lawn Mowers, etc.): Back fireing on briggs, head gasket leak, briggs and stratton

Question
Hi eric I have a Briggs and stratton twin cylinder that is back fireing threw the exhaust What would cause this and what should I do too fix it? I have replaced both spark plugs and have check the flywheel key and have check the armature to see if the coil is fireing. also do I need to check the valves or would this be in the carb? someone told me this Thanks Alan

Answer
How old is the engine?  Will the engine start and run at all?

Most of the time backfiring is caused by either the igntion timing,(flywheel key), running lean,(carb, intake or head gasket leak), or overheating which could be valve related.  Rarely do those large engines shear keys.

Let me know the answers to the questions so we can narrow down the problem.
Eric