GEEEZ man, that thing sounds like a "thrashing-machine" when starting, sounds like the starter is grinding, but then again, it sounds like the pistons are dragging in the cylinders, did it run out of oil ?? or overheat ?? you say you replaced the starter,.. is it the correct model, (pinion-gear ??) I would pull the plugs and with a strong flashlight, look in the cylinders for scored walls, does it rotate EASILY by hand with the plugs removed ?? In my opinion you have a SERIOUS issue with that engine, and why the huge start cart, will it attempt to start with a fully charged mower battery ?? IF you need that many Amps to roll it over you DO have a problem !!