Oddly enough I did exactly the same to our Briggs and Stratton lawnmower a couple of weekends ago.
It was running lumpy and sounding like it wanted to stop when meeting a slightly clumpy section of grass, so I decided to give it the first service*
Replaced the gasket and diaphragm, plug, air filter and oil. Full service for under £10 (excluding oil, which I had from a previous car)
Very satisfying when it roared back into life like a demented go-kart and no longer slows down for anything.
* or 17 years since purchased, what ever occurs first.