John Deere RX75 quits after 20-30 minutes

[Oddjob]

This rear engine mower has a 9HP Kawasaki. It starts easily and runs smoothly until it gets hot. I replaced the igniter and still have the issue. I have driven it with a spark tester attached and it does have spark right after it quits. I also sprayed carb cleaner into the carb right after it quit and it starts and runs until the carb cleaner is burned off. Twenty minutes after it quits, it will restart and run for about 10 minutes. So I think it is likely that I have a fuel issue brought on by heat. No fuel pump on this model, it is gravity fed. I replaced the fuel lines and filter and carburetor. I can see fuel in the filter. I guess it is possible that the spark is weak and will ignite carb spray but not gas, but this seems unlikely.

There was a service bulletin listed in the technical manual for this mower for quitting when hot but I can’t find it on the web and John Deere has not responded to my request for a copy. Anyone have a copy or know where I can get one? Has anyone had this problem and fixed it? Any ideas?

 

[GearHead36]

Next time it does this... loosen the gas cap. Could be a bad vent on the cap. Check the cooling fins. Maybe it's overheating. Disconnect the fuel line at the carb, and see if you get decent fuel flow. It could be that there's a restriction in the tank or fuel line.

 

[Oddjob]

Next time it does this... loosen the gas cap. Could be a bad vent on the cap. Check the cooling fins. Maybe it's overheating. Disconnect the fuel line at the carb, and see if you get decent fuel flow. It could be that there's a restriction in the tank or fuel line.

Thanks. Should have mentioned that I already took the fuel cap off. The fins are clean. Since it starts and runs with a spray of carb cleaner, I am thinking there is something going wrong in the carb.

 

[Oddjob]

Update. Problem solved. I noticed that sometimes when the key would not energize the starter circuit that slightly moving the PTO lever (inconveniently too close to the key) would cure the problem. That got me thinking about the viability of the safety switch for the PTO, (which is actually a two way safety switch for the transmission). I pulled it off and tested for continuity. The transmission part worked fine but the PTO switch was hinky. With the button fully depressed there was no continuity but with it about halfway depressed, it completed the circuit. The more I tested it the more erratic it acted. I replaced the switch with the oem JD part. I just finished mowing front and back yards and no stalling. It is 72 degrees here today, so warm enough to rule out an environmental cure for overheating. I think the switch was failing and the heat from the current going through that safety caused an open circuit when the button on the switch was fully engaged.

I am not very experienced with riding mowers and wondering if this sort of switch failure due to heat is common?