Lawnmower starts then cuts off.?

It's very common for the float needle to stick in the o-ring it seats in to shut off the gas. that mey be happening.

With it shutting off in 2 seconds I suspect that the ethanol in the gas has caused the o-ring to swell up to the point the o-ring hasn't got a hole open in the middle anymore and either needs replacing or you can try using a small drill bit to ream the o-ring hole out. Do it by hand...don't use a drill to power the drill bit. You nay need to reset the float height after reaming the o-ring if gas leaks out of the carb by the air filter.

I had to finally buy a new carb this year after reaming out the o-ring 3 years in a row. I found that buying a new carb on ebay cost $13.79 and was even cheaper then trying to by a rebuild kit for the old carb. Shipping was even free!

The carburetor is brand new. It's almost completely impossible it's water in it. Could there be water somewhere else or a vacuum leak? It's certainly not in the carb if its water.