This thing is going to drive me nuts! She used it for several more hours, then took it to my son's house and it promptly crapped-out. Again, seems like no spark and definitely no joy with starting-fluid. I have been testing for spark with a new plug, but it is an automotive resistor plug. I'll get a new mower plug, just to get past the possibility that the resistance in the new plug is confusing the issue. To recap: I have two inop mowers, this one with "no spark" at times, and the other with a leaky carb. Both can run fine, so I doubt there is anything seriously wrong with the innards (piston, rings, valves) of either. The "bad carb" one will start, using starting-fluid, with either of the cruddy mower plugs. The "bad spark" one won't fire at all (again, starting-fluid) with either plug, when it is "not in the mood". Neither engine seems to have a good spark. In fact, most often I can't see any; yet the "bad carb" one always fires. When I can see a spark, it is very apparent, I don't think this is just a matter of the sun-light being too bright... This is the world's simplest ignition system, just that coil and flying magnets on the flywheel. I have disconnected the "kill wire" right at the coil. it seems absurd tostart probing with scope to see what is going on with the coil when I crank it, but I guess that is where I am headed after the new (mower) plug doesn't do any good. My wife and son are going to quickly force buying of a new mower if I can't make headway here, which seems equally absurd, since these beasts can run.