Help Briggs & Stratton Sprint 40

Hi I Have A Briggs Spint 40 On A Lawnmower Which I Was Given
It Starts Ok But Seems To Pop From The Exhust When Runing?

Any Help Will Be A Great?

Thanks
Bill

Old fuel, dirty air filter, bad diaphragm in the carburetor. Some of these engines with a very small muffler are just prone to a little popping out the exhaust.

Thanks For The Help Just Ordered New Diaphram & Primer Kit See How This Works

Thanks Once Again For The Advice

Bill