The thought did cross my mind, but then I dismissed it. I have that problem with Honda small engines sometimes. wasn't sure if that was possible with a Briggs. I'll take one off of a display unit and try that. thank youFuel tank cap vent working? Try running with cap off.
If yours is fitted with the Briggs 800 series engine then it could be the drilling from the fuel pipe connector at the tank.
Had 1 where the hole wasnt big enough and also one where plastic from the drilling had not been cleared and got into filter and some cases the carb itself.