I mowed an acre, it began to lose power as I was finishing the area. I ran it up on the cleanout stand, washed the underside of the deck, like I always do, tried to start it to put it away, no start. Hearing the fuel pump running, I turned it off, opened the hydrostatic relief valve and towed it to the shop with the wife's GX345 and began the diagnosis.
No spark, checked fuses, power to the coil, checked the plugs, etc. I pawed through the "425 Parts" box, found an old ignitor and an old delay module. Not wanting to waste a lot of time, I did something I've warned others about for many years. I replaced both components before checking for spark again. Not good, what now!
I put the original ignitor back on, still no spark, put the used replacement ignitor back on, took the replacement delay module off, put the original module back on, now it starts & runs good! Long story made short, two defective components, one in the spare parts box and one on the tractor, swap them going back & forth at the same time and the result is the same, no spark.
Lesson in all of this....if you're going to stand back and "shotgun parts", just replace one part at a time, if it doesn't provide the desired results, throw another one at it, repeat as necessary..
I would never purchase new parts while using this method, but...with a box full of used junk, sometimes it works...