I have a 1994 John Deere 425 with the Kawasaki FD620D engine. I have owned it for a little over a year and it has about 740 hours. I mow 3+ acres with it. When I got it I replaced all fluids and filters, and I've put about 100 hours on it. Last year it ran flawlessly through some pretty demanding work.
This spring it started acting up. When I hit a bump it would start to die and then recover. I found that the red wire to the starter solenoid was a little loose. I clamped down the terminal end a bit on the wire and that seemed to help for a while. But then the problem returned and got worse. It would run pretty good...but not as smooth as it used to...for a while (maybe 30 minutes) and then start sputtering. Worse on bumpy terrain, but not exclusive to that. It was also running hotter. Not in the red, but definitely higher in the green than I ever saw it get last year. I searched forums and found some people describing similar troubles, and the two common culprits seemed to be the Time Delay Module and the thermostat. I replaced the Time Delay Module and it didn't fix the problem (but the tractor does shut down more smoothly now). Yesterday I replaced the thermostat with a Hypertech 1003 160 degree thermostat, and I flushed and replaced the coolant. That seems to have helped some, and for a while the tractor ran as smoothly as I remember it running last year. The temperature gauge stayed in the lower 10-20% of the green area. After half an hour or so the temperature started climbing noticeably, but the tractor still ran fine. I finished mowing the area I was in, shut off the PTO, and lowered the throttle to half while I drove back to the shop. Shortly after I lowered the throttle it started sputtering. If I raised the throttle to full it was fine, and if I just sat with it at half or lower it was fine, but if I tried to drive the tractor with the throttle at less than half or so, it sputtered and nearly died.
One other note...I have the air cleaner indicator gauge on it, and it shows a normal reading. The air filter cover says not to disturb it if the gauge reading is good, but I opened it up anyway. There was a ton of dust in there, which I cleaned out. That was about a month ago. As with other attempts, it seemed to help a little but didn't solve the problem.
Anyone have any good ideas for me? Just wanted to do what I could before I take it to the dealer. I thought it might be difficult for them to troubleshoot since you have to mow with it for a while before the trouble starts to show up.
Thanks for the help!