Run the mower until it quits, then turn the key on and off, and listen for the fuel solenoid on the carb. You should hear it click when you turn on and off. If it doesn't click then that is most likely the problem. The other thing to look for is. If you turn the key off and back on, and you hear the click, then immediately start the mower, it is possible that the plastic tip on the solenoid plunger is coming loose, and stopping the fuel flow.