ORIGINAL: Lifer
Thanks for the replies, but I still have the same question: How can it produce a spark but not allow the engine to fire? I replaced the old unit with a new one and it fired right up. Again, does anyone know how the old one can spark, but not support the engine to run?
If the ignition has a choice of firing across the gap in a plug, as well as something requiring slightly more power (say a leak within the spark plug boot, or a coil that's starting to break down internally?), the extra power required to fire the plug at the top of the compression stroke can make the difference between which path offers the least resistance for the spark to get to ground? It is not THAT unusual to have a plug fire when outside of the cylinder, but not while under compression.
Other symptoms might include an infrequent pop or 2, exhaust smoke, back firing, etc. This has happened to me twice now, and replacing the spark plug boot has fixed the problem both times. -Al