u/Familiar-Remove-449

I have an 11 hp Briggs L head engine that about rips my fingers off when trying to start. It seems like a timing problem. I changed the flywheel key, bought new valves and ground to spec, and replaced the starter clutch with no change. I disassembled the engine, checked if the timing marks were aligned, measured the cam lobes, and checked for a broken compression release. reassembled and the same thing. Any thoughts?