This year started great. Early, before the last frost, I used the mower to haul my sprayer around the yard. The spray killed the winter grasses that were tough and prolithic and tended to crowd out the Bermuda grass. The winter grass was nearly gone by the first time I cut the lawn. Several more mowing episodes followed with the lawnmower doing what one would expect mowers to do. Absolutely no problems, no hint of complaint. Then Kathy and I were were gone for a week, traveling west to visit my brother Bill who was in an Amarillo, TX hospital. During that week, the yard received six or eight inches of rain and summer came with 90 plus degree temperatures. The grass grew tall.
Mowing was high on my tado list when we returned, but my mower refused to cooperate, commencing to gasp and sputter after cutting grass for thirty minutes or so. I did notice that if I mowed at night when it was cooler, the mower worked better. The cooler the temperature or the lighter the load on the engine, the longer it would run without failing. This on again/off again action meant that if I took it to a repair place, they'd probably not discover the problem unless they went to considerable time and effort. That was okay. My time was cheap. Plus, I had a service manual and wanted to solve the problem myself..
The first thing I checked was the fuel filter, then I put fuel treatment in the gas tank. Water in the fuel can sometimes cause failure like I was having. It could also be a dirty carburetor, but I knew the carburetor was okay because I overhauled it last summer. The failure continued after changing the fuel filter and treating the gasoline. I diagnosed the failure as an electrical component problem because it had the characteristics of a heat-sensitive semiconductor. I'd seen plenty of those at work. If I was right, this meant there were five possibilities for failure: the submerged electrical fuel pump, the coil modules, two of these, one for each cylinder, the ignitor module, the ignition delay module. This last component was used to keep the engine from backfiring when it was shut down.
A search on the Internet discovered the heat-sensitive failure was a common one for my mower, a John Deere 425. There was little consensus on a single solution. Since the failure only occurred when the mower was hot and under a load, I had to troubleshoot it 'on the run.' I spent considerable time on the mower peering through the steering wheel and trying to see the dim (in the sunlight) glow of an in-line spark detector before I determined that it was not the coil modules. I bought a cheap fuel pressure meter and installed it in the fuel line. No failure there so the fuel pump was okay. This left the expensive igniter and the less expensive ignition delay module. They were connected in series and were impossible to diagnose separately. I bought and installed the cheaper one and still had the failure.
The $275 plus tax John Deere wanted for the ignitor module seemed a bit pricey so I decided to explore alternatives on the Internet. The engine was made by Kawasaki. There was part number on the ignitor, but the module was underneath, hard to get to, and the print was small. I solved that by using a camera and reading the part number from the enlarged photo.
I found the ignitor module on the Internet for under $100. Installing it without pulling the engine was a real struggle, but I managed to do it.
Did it solve my problem?. It appears so. More testing is needed.