Help with the lawnmower. It starts and stalls after a few seconds

Let warm up if still does need new spark plug

need to load test the batteries --and test amp draw to the motor look under dek and make sure no debris is caught around the blade shaft --can cause over heating of motor

remove and clean carb , change fuel filter , check fuel tank for obstructions ,is there a problem with choke

Have you checked the fuel supply first. Its possible your jet valve may be plugged or dirt in the fuel bowl. One quick way of checking this is take the spark plug out and put a little shot of gas in the spark plug hole then reinstall the spark plug and put wire back in place and try to start engine. If it start and revs up for a few seconds till the gas is burnt up then stalls it is pretty certain its a dirty fuel jet or dirt in the fuel bowl. This quite often a real cheap fix .

If ir starts and runs for only a few seconds it's a dirty carb/bad gas. Drain the fuel system and use FRESH gas; change out your fuel supply monthly to avoid "phase separation" issues. If it runs for several minutes and then dies it is possibly a sticking valve. Do a compression check cold and after it stalls to confirm. Hope this helps

I will need a few more details about your no start condition. Does the engine just click or does it turn over and just won't start? What are your battery amps? Did you check for spark? Do you have fuel?

it sounds like the carby main jet is blocked you real need to take it to a mover shop as It is a tricky think to clean out there are jets on them that are hard to find ,pin hole size

Bad fuel or check for water in your fuel! Clean your carb and float bowl. Empty gas into a clear container, if there is two levels of liquid one of them is water. Of course make sure you have good spark plug.

Adjusted the spring to the choke

sounds like a bad coil/magneto.