what is wrong with my lawn mower?
Briggs and Stratton engine, model # 12Q802 Type 0204.
It runs for 5 minutes and dies like it is out of gas. Sometimes it will crank again for a few seconds if you prime it 10 or more times, sometimes it won't.
Either way, if you let it sit overnight, it will crank up immediately and run for another 5 minutes and the cycle repeats. It will take a month to cut my grass this way.
The gas cap did not have a vent in it, so I drilled a little hole in it. I mowed half the lawn in 30 minutes and it didn't die at all - even in the thicker grass. I will finish it in the heat of the day tomorrow to see if the temperature has anything to do with it.
Thank you for all of the answers so far.