Engine z445 dies after 10 minutes

to me sounds like a couple of problems.
1) some corrosion around the throttle butterfly shaft or debris on the throttle butterfly itself
This would be preventing the butterfly closing down so you always are on 75% running speed.

2) the governor arm is not adjusted properly on the governor shaft that pokes out the engine.

3) the spring that connects the throttle control to the governor is weak or in the wrong position.

How much corrosion you get inside a standing engine will depend upon the microclimate at the position where you store the mower.

Sounds like the governor is working but check this by starting the engine and working the throttle using your finger on the rod on the governor arm .
If you opened it and the engine speeds up smoothly and then drops down to the 75% speed whenever you let go then the governor is working

If it feels rough when it moves then the carb probably needs a clean around the throttle.

And of course as Will has already mentioned check that the throttle stop has not been adjusted too far preventing the throttle returning to the fully closed position.

Got it fixed, the throttle arm of the choke was caught on the little nubs that stick out on the side of the heat separator for the gasket, turned it around and now it operates normally. Not sure what purpose those little nubs server other than to get in the way.