Small Engines (Lawn Mowers, etc.): Plugs foul - firing shooting out exhaust, briggs stratton, magneto

Question
I have a Briggs & Stratton 16hp vanguard v-twin engine; running rich.  Every time plugs are replaced runs fine for about 30 minutes when plugs foul, then I get fire through the exhaust.

Answer
Hi Pat
 The fire from the exhaust is a result of the plug misfiring and when it does fire, it is burning the extra fuel in the chamber or it could be valves out of adjustment. Check your flywheel magnet and magneto arms for rust and trash buildup which could cause a misfire and/or a weak spark. Also check your carb jets and ports to make sure all are open and unobstructed. Hope this helps.