I have a Briggs and Stratton 15.5 hp that is kicking extremely hard back against the starter. I checked the flywheel key and it is in excellent shape. I changed the ignition coil out with one I had in stock and still have the same problem. I checked the valves and the intake is .004 and the exhaust is .006 and the ignition coil was set at .012 when I changed it out.