Why does my mower die after mowing for 20 minutes Does it have a breaker?

It could be a gas problem or an electrical problem.

There is a fuse on most riding mowers but no circuit breaker.

I am assuming that it will not re-start after it dies....

The first thing to try is to make sure that the vent in the gas cap is clear. Many times when filling the gas tank people lay the cap on the ground and it gets caked up with dirt in the vent hole. It will cause these symptoms. Just use a paperclip or blow compressed air through the hole to clear it out.

If that doesn't help try running it until it dies and then remove the air filter, spray some carburetor cleaner directly into the carburetor and see if it runs on that. Chances are that it will not. If it does them you have a gas related problem. If it doesn't then it is electrical.

If it doesn't not run then it is probably loosing spark. The coil is proabably getting hot and breaking down.

Try these things and see if you can identify the problem then get back with details...