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.

Hi,
Remove your valve cover and make sure that the rocker arms move the same amount when the engine turns over. A few years ago there were bad camshafts that wore prematurely on the exhaust lobe.
Peace,
Clarke

Thank you Clarke, this joker about had me pulling what little hair I have left out. I got two same model 15.5 hp in my shop this one that is kicking back and not starting and another that starts and runs as beautiful as can be without a load, but immediately dies when you put a load on it.