first of all i would run the engine at idle for 10 or 15 mins and then drain the oil. The Brigg and stratton or aspera^s dont have filters like moter cars-
Then i would remove the plug and spray some WD 40 or other good spray oil into the plug hole and let it settle to release the rings from the crud that has collected orver the time.
check the valve clearances as they do wear and increase the gap.
clean the plug and regap it, clean the air intake and especially the air filter maybe if it is soaked in oil was and rinse and then reoil.
check the blades are not dragging like Englishman said cos of string dried grass etc.
another thing is replace the oil with a detergent oil which will also clear the crap inside the motor.
1. the practice of professing standards, beliefs, etc., contrary to one's real character or actual behaviour, esp the pretence of virtue and piety
2. the condition of a person pretending to be something he is not, especially in the area of morals or religion; a false presentation of belief or feeling
now if you understand that, you will see by my comment i am not the hypocrite ut you are.
gussi Forum Posts (4,032)
the wine is plenty 
bonus
stop patronising or is it flirting i dont know
( the flowers)
RE: PollyWolly's London's Coffee Corner...Part 5..
So bye bye ladies pleasure was mine