Was cutting the grass and the engine stopped.
Tried to restart but cannot. The battery is fine, the oil was just changed, the gas is clean and fresh, the carburetor is clean, the air filter is clean, the choke works fine, the spark plugs are clean and dry. The enine turns but won't fire up.

Check that the connection to the fuel solenoid on the carb has not fallen off. If OK, you need to eliminate check if you have an ingnition or a fuel problem.

Remove the air cleaner. While someone cranks the engine, spray some carb cleaner into the air intake. F the engine fires, you have a fuel problem. If not, you have an ignition problem.