Small Engines (Lawn Mowers, etc.): Z Mower motor bogs down and wants to choke out, high grass, winter storage

Question
I have a Toro Z5000 Riding Mower model 74370.  The mower works fine until it gets hot.  After mowing for approx. 15 mins.  the motor wants to bog down as if you had the deck too low in high grass.  After turning the deck off the tractor runs fine.  Only messes up with the mower in operation.  If you stop and let it cool down..you can mow for 15 mins and you have to stop again....any ideas?????

Answer
Below is the link to manuals for your mower:

https://homeownersolutions.toro.com/portal/server.pt/community/product_center/225#manualsResultPage

Just type in the model number.

Will the mower run for more than 15 minutes with the blades off?  Did you just get the mower out of winter storage or have you used the mower a few times this summer?  Did the mower run alright when you got it out after winter storage?

Are the engine cooling fins clean, no debris clogging the cooling fins?  You will have to remove the top engine shroud to check the cooling fins and flywheel fan.

Very interesting problem.  Could be something simple but may take a while to isolate.  Do you have a multimeter to check/measure voltage and resistance?

Eric