Your symptoms sound like a spark plug. Remove the plug wire and use a socket wrench or an adjustable wrench and unscrew the plug out. Get the numbers off it or take it in to purchase a new one.

Also make sure you have the proper oil level, too much, or too little will be chaotic on the engine. If you put too much oil in reservoir it could of fouled your plug up (ie end of plug will be tar black) making it not wanting to start or stalling

If you think you put bad gas in it just turn the mower on its side, cap off, and drain the tank dry, and then put new gas in it.
10-15 minutes to do both.

Good luck

RD

If it has a choke feature, make sure you are taking the choke off after it starts, I’ve seen people who left it on and it can make the mower run like crap (or stall).

It could be a loose muffler, wait until the mower is cold and make sure the muffler is on good (make sure all the screws are tight). If the hot exaust can’t get out of the engine it creates back pressure on the valves which can stall the engine or make it run poorly.

It could also be a cracked block, if this is the case the mower is shot and you should return it before the warrenty expires. What happens is as the metal heats up, it expands, so the crack opens up. this allows the pressure in the cylinder to vent through the crack, rather than pushing the piston down, therefore the engine runs poorly or stalls.

You might also try completely draining the gas tank and filling it with fresh gas. If it sat in a shed over the winter, there could be water in the gas. after it runs a few minutes the water gets stirred into the gas and makes its way into the engine causing it to stall.