My 255 John Deere mower dies after I've been mowing about ten minutes and has no fire at all. After it has completely cooled off it starts right up but will just die again after it has gotten warmed up. Is this possibly the electronic ignition going out? When it dies I've held plug wire and ground and there's no spark at all and once it cools off and will start the spark still isn't very strong. I've changed plug. Any suggestions?

I think you hit the nail on the head.

Sounds as though the coil (armature-magneto) is breaking down from the heat generated inside it. Replace the coil, at least that is the best advice I can give by the info presented here. You can use a business card to set the gap between the magnets on the flywheel and the new coil.