Remove the float bowl.
If the bowl is full of fuel then the solenoid in the float bowl if not retracting .
Check that you are getting voltage to the plug .
Usually you can soak the solenoid in carb cleaner , WD 40 or similar and work the plunger till you get the crud that is making it stick out .
OR you can chop off the plunger which is ILLEGAL in many places & has big fines for doing so.
It will also cause the mower to backfire through the exhaust when shut down
OR you can replace it but is it worth 3 cases of beer ?