May be that there is water in the tank (perhaps from dew condensation).

harry manka wrote:
My 5-6 year old lawn mower with Briggs & Stratton 4.5 HP engine is
acting up. Worked fine until yesterday when I refilled it with gas and
now it starts but engine stops in 2-3 seconds. Checked/cleaned the
plug and checked oil. Could it be that gas line is clogged and engine
is not getting continuous supply of gas? Any thoughts? thanks.

Harry