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I've got a Kawasaki FH680V in my zero turn mower that apparently overheats and shuts off after 40 minutes of mowing.

I've changed the fuel lines, filter, solenoid and pump as well as the spark plugs. The gas caps are relatively new and are vented and clean. It does surge when the PTO is disengaged but runs fine when mowing. I'm told I need a new carb.

When it shuts off does the engine sputter and run rough before dying or does it die like the key was turned off I am wondering if it fuel or spark related

When the engine is surging, slowly apply the choke. If the engine begins to smooth out then I would start with cleaning the card. There is likely no reason to replace the carb if the engine otherwise runs well.

ILENGINE said:

When it shuts off does the engine sputter and run rough before dying or does it die like the key was turned off I am wondering if it fuel or spark related

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It shuts off all at once. No sputtering. Also, I forgot to mention, the first thing I did was to remove the shrouds and clean everything.

Shuts off all at once leads me to think the issue is not fuel related but more igntion related. Loosing spark when something gets hot.

It is not likely to loose both ignition coils at once. If one is lost the engine would continue to run unless potentially it is under heavy load. My thought is either losing power to the fuel solenoid or it is something in the safety system on the mower. Still, the surge when disengaging the PTO is likey due to the carb needing to be cleaned.

txmowman said:

It is not likely to loose both ignition coils at once. If one is lost the engine would continue to run unless potentially it is under heavy load. My thought is either losing power to the fuel solenoid or it is something in the safety system on the mower. Still, the surge when disengaging the PTO is likey due to the carb needing to be cleaned.

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Crosstalk diode in one module failing can potentially shut down both modules. Wouldn't be the first I have seen on Kawasaki engines. And we don't have the spec number for the engine or what brand of equipment it is mounted on.

ILENGINE said:

Crosstalk diode in one module failing can potentially shut down both modules. Wouldn't be the first I have seen on Kawasaki engines. And we don't have the spec number for the engine or what brand of equipment it is mounted on.

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Sorry, this is false. A failed diode on one coil would cause the opposite coil to show as failed. Two failed diodes would cause the coils to not be able to be grounded through the key switch.

txmowman said:

Sorry, this is false. A failed diode on one coil would cause the opposite coil to show as failed. Two failed diodes would cause the coils to not be able to be grounded through the key switch.

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So what is happening when I disconnect a kill wire from either coil, and both spark, but if you reconnect the kill wire to both coils neither will spark. Or have the engine running and ground one spark plug wire and the engine dies. Restart the engine and ground the opposite spark plug and the engine still dies. The only place I have experienced this on multiple engine over the years is on Kawasaki.

ILENGINE said:

So what is happening when I disconnect a kill wire from either coil, and both spark, but if you reconnect the kill wire to both coils neither will spark. Or have the engine running and ground one spark plug wire and the engine dies. Restart the engine and ground the opposite spark plug and the engine still dies. The only place I have experienced this on multiple engine over the years is on Kawasaki.

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It means that there is a failed diode in one coil. If for example, the number one coil has a failed diode, coil number 2 will not have spark. The diode, being a one-way check valve, if failed will allow the opposite coil to find a path to ground through the failed diode. In your example, if neither coil will spark with the ground wire connected, then the ground wire or key switch would be the failed part. On the second example, if this scenario happens with the ground wire disconnected, it could be weak coils or the air gap being out of spec. This would be a very rare event. Definitely not a common occurance.

txmowman said:

if neither coil will spark with the ground wire connected, then the ground wire or key switch would be the failed part.

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And if I replace the coils the problem goes away. See it at least once or twice a year. And in your scenario the coil that is still connected to the ground wire would still not have spark. But if I disconnect one coil they both will have spark including the one that should be grounded through the faulty ground wire or key switch in your explanation.

txmowman said:

On the second example, if this scenario happens with the ground wire disconnected, it could be weak coils or the air gap being out of spec. This would be a very rare event. Definitely not a common occurance.

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I suspect weak coil, but for me it is common enough that I see annually Normally shows after a rain or heavy dew. In all cases the epoxy will have cracks which could result in moisture intrusion.