Hello UAMES
Your John Deere 14SZ has the Briggs & Stratton engine on it. You should be able to replace the Magnatron ignition coil being the very same one used on all Briggs & Stratton engines fairly reasonably. I surmise this is your Problem is an Ignition coil as when they get warm they Often fail and quit making spark or progeress to Not sparking at all when cold. I hope this helps, Hammerdown