Small Engines (Lawn Mowers, etc.): 4 stroke lawn mower engines, lawn mower engines, mower blade

Question
what generally causes a lawn mower engine to kick back violently pulling the pull cord out of your hand and almost starting? I have 2 Sears machines both doing the same thing they are Briggs Engies small 4.75 hp. Thanks, Jay

Answer
The engine is out of time you probably have a broken flywheel key.  This is a very simple repair.  Remove the blower housing which is the hosing starter attaches to remove the flywheel nut pop the flywheel off and replaced the key.  But the flywheel back on and torque than nut very tightly.  You will have to use a block of wood to stop the engine from turning when you remove or reinstall the flywheel nut.  The block of wood would be placed between the mower blade and housing.