Bought a used 1996 721D a few years ago, 1500 hours, mow a couple of acres a week, no issues to speak of. Recently it dies randomly while mowing. Engage the starter and starts right back up. Mow for a while and it happens again. Does not lose power (rpms) before it dies. Watching the temp gauge, not overheating but it seems to happen more frequently after it has run for a while. Replaced fuel filters after first episode and initially thought it was resolved but not so. Airfilter new and I blow the machine off with air every time I use it including radiator and Rad guard .Bypassed the kill switch under the seat. I suspect there are other safety kill switches but I don't have a manual so I am not sure about where to look.
I have a 321d and it was doing something similar. I store my mower in the barn and it seems the mice like to use it as a home. They chewed the wires on the mower controls. I had to replace a bunch of wires (I also built a cage around the controls out of hardware cloth to try and keep them out). Take a look at your wires and make sure everything is connected well and no wires are frayed. Good luck
