Diagnosis of these kinds of complaints are VERY VERY hard to do online, and most of the time even over the phone.
Now, that said, get on your mower, go make it act up. As soon as it starts to bog/die (if I am understanding correctly it does that right?), reach over and push the choke lever to "choke". Does the engine then increase power and speed? If yes, you have a fuel problem of some sort. If no, you likely have either a mechanical problem or engine problem or perhaps electrical problem.
The safety switches on the control arms work the minute you move the arms from "out" to "in", only have to move them maybe an inch at the most. With parking brake ON, move the arms slowly from out (neutral) to in. Engine should die as you move each arm away from "neutral". IF they do that, then the switches are working properly. Very very rare to have a control arm switch fail because of where Kubota installed them and how they installed them. Seat switch failure is also very rare on the Z700 series. Brake switch sometimes, not often. Not rare but not often. HOWEVER; the brake itself sometimes sticks partially down which makes the system "think" that the brake is on, thus as soon as you move the control arms, the engine will die. To test, the next time it dies while in operation, reach under the brake pedal with your toe and pull the brake pedal up towards you. Does it pick back up and run properly? Yes=lubricate brake shaft. No=you have a different problem.
The good news is that they're fairly simple. The bad news: Kohler. I hate Kohler. Ignition coils and starters have been very very common failure parts as of the last year or so, maybe it's because so may machines are coming with Kohlers, I don't know....I have a stack of starters at the shop, and probably half that stack of ignition coils, specifically DSAI coils but also a few MDI's. I'd just as soon have a kawasaki and actually I may end up converting my ZG127 to a kawasaki now that I've got a selection of engines to choose from (all need repair).
