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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.

My Toro started dying after an hour, thought that was overheating but turned out to be dead insects in the fuel tank. Somehow despite all the bouncing around they somehow took almost exactly the same time to block the fuel outlet each time. No I didn't believe it either but that was definitely it. Thing is the bugs were bleached so hard to see. Soon as I drained the tank and dried it out I could see a few. Vacuumed them out and the mower worked faultlessly afterwards. It did the same the following year and the solution was the same. I discovered they were getting into my Jerry can spout and then being flushed into the tank when I filled up. Now I keep it in a bag.

When it shuts off the first thing I would do is check for spark on the ignition coils and second see if the fuel solenoid piston is pulling down and staying down as long as power is applied.

djg618 said:

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.

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How do you know it "overheats"?

ILENGINE said:

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.

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On my 731 the plug leads are carbon track type....meaning they have a carbon impregnated string carrying the electricity to the plug. I cut the rubber boot off and found that the cap had not been fully crimped to the lead and did not contact the carbon string. Replaced both caps with these...


There is a 3/4 inch (appx) screw in the boot that gets turned up into the carbon string core to make contact. Fixed immediately. There is also a tendency for the carbon to migrate within the core and sometimes leads to a drastic reduction in energy delivered. This is but one possibility, not necessarily your problem.

Also....losing one cylinder does not mean you lose 50% power, it's more like 75% with all the dead pumping losses added. Losing a cylinder while under load results in stoppage, generally.

RevB said:

How do you know it "overheats"?

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It feels a lot hotter when it dies. True this could just be the effect of the run time. Plus, on another forum, it was brought up that gas starvation, either due to a dirty carb or plugged fuel line/filter/tank would cause the engine to run hotter, thus causing a vapor lock in the fuel system. So I am told. That's why I've been fixated on the carb. That and the surging.

Thanks everyone for your replies. I'm not going to reply to each individually, but I do appreciate your ideas and am going to look into each one.

I'll be mowing again Monday or Tuesday. Tomorrow looks dry, so I'll roll out the mower and do a few things to it. Me and the previous owner never used the Left tank so I'm going to block it off with shut-off valves I have, drain, remove, inspect and flush it out. I'll do the same to the fuel line and filter. Reinstall and use only this tank to the carb. If it dies, that is ruled out. If it doesn't die, I'll repeat the cleaning process with the primary tank.

If it does die, I'll check the spark on both plugs (new). I have one of the testers that you hook up; I'll just have to read up on how to use it. If I don't have proper spark on one or both, I'll order a new set of coils.

If I have to install new coils, and it still dies. I'll finish the yard in sessions as I am doing now and the remove the carb and clean it. I'll check that out on the following week. If it still dies, then a new carb.

Did I miss anything?

Thanks

P.S. Forgot to mention, the solenoid is new.

I have an FT730V that had a similar problem. Discovered the cooling fins were about 50% clogged with dirt and grass. My bad for not seeing that sooner. Anyway, cleaned them, and replaced the temperature sensor (EFI engine). No more an issue. Don't forget to check the fins inside the shroud.

I have an FT730V that had a similar problem. Discovered the cooling fins were about 50% clogged with dirt and grass. My bad for not seeing that sooner. Anyway, cleaned them, and replaced the temperature sensor (EFI engine). No more an issue. Don't forget to check the fins inside the shroud.

djg618 said:

It feels a lot hotter when it dies. True this could just be the effect of the run time. Plus, on another forum, it was brought up that gas starvation, either due to a dirty carb or plugged fuel line/filter/tank would cause the engine to run hotter, thus causing a vapor lock in the fuel system. So I am told. That's why I've been fixated on the carb. That and the surging.

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An inexpensive IR thermal gun is worth its weight when diagnosing some problems. Objective measurement beats subjective measurements every time.

Well...that's just not true. As an aviator of injected engines, you may have the capability to run rich of peak EGT or lean of peak EGT......rich uses excess fuel to cool an engine, lean uses excess air to cool the engine. Air is free and does not contaminate crankcase oil nor leave excess carbon. Even a carbureted engine has the ability, tho much more limited, to do the same thing. Years ago someone attributed an engine failure to lean combustion and "burned valves"....the only way you get burned valves or seats is to hold the valve faces off the seat and let combustion gasses erode either one....most likely the valve because thermal mass is much less and the valve gets hotter than the seat which is very effective at shedding excess heat thru the head's mass.

RevB said:

An inexpensive IR thermal gun is worth its weight when diagnosing some problems. Objective measurement beats subjective measurements every time.

Well...that's just not true. As an aviator of injected engines, you may have the capability to run rich of peak EGT or lean of peak EGT......rich uses excess fuel to cool an engine, lean uses excess air to cool the engine. Air is free and does not contaminate crankcase oil nor leave excess carbon. Even a carbureted engine has the ability, tho much more limited, to do the same thing. Years ago someone attributed an engine failure to lean combustion and "burned valves"....the only way you get burned valves or seats is to hold the valve faces off the seat and let combustion gasses erode either one....most likely the valve because thermal mass is much less and the valve gets hotter than the seat which is very effective at shedding excess heat thru the head's mass.

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Almost forgot....the old spark testers were just neon bulbs in a non conductive pen except for a cupped aluminum cap that fit over the plug wire. If the bulb lit up, spark. Also useful to check electric fences to see if they're on or not.

Poor pto switch or connection at the pto switch will turn off engine, so will a poor contact at the 20 amp fuse that feeds the mower from the battery. Try checking these for possible porblems.

Poor pto switch or connection at the pto switch will turn off engine, so will a poor contact at the 20 amp fuse that feeds the mower from the battery. Try checking these for possible problems.