While you wait for answers, we may have found some information which could help you.
Click here for Replace Briggs EngineAdding oil to mower ?
lawn mower won't start?
My Briggs & Stratton 10.5 engine will start but dies after about 15 mins?
lawn mower engine hunting?
How can I fix Mountfield Laser Omega 46 Lawnmower?
my briggs and stratton 3.5hp starts up then cuts out straight away?