As I said in my advice above. If you have doubts try a KNOWN good plug in the engine. This should actually be one of the first things that is tried when and engine is hard to start. I can't even begin to count the number of times I have seen guys sit there and try over and over to start a dead engine. They fiddle with the needle valves. They defuel and refuel. They will do any number of things. But they never change the plug. When they FINALLY get around to trying a new plane the engine will "magically" roar to life.

Now this applies to starting an engine. An engine dying in flight will usually not restart, so it should be a very quick (if you follow my advice about trying a new plug first) fix to put a new plug in. Or in my case today with a dead stick. Then engine would only run with the glow driver on. I swapped the plug and was back flying in a couple of minutes.

Ken