G'day starbio7,
With regards to both NormK's and Max's replies, they are both correct, and I would also like to add my thoughts on this matter.
[Remember Rule#1:- Before you do anything on your mower, always remove the rubber grommet cover from the spark plug] 
Having said that, have you considered draining all the existing engine oil out, and replacing it with a new supply, of the same?
[e.g. when I do my mowers, I measure how much is drained into a container, weather it be 15W 30, 40, or 50 e.g., and the amount that comes out, a new supply of the same amount goes back in, with a small top up if necessary]. As Max says, don't over fill it!. Also,  remove the existing spark plug [the # should be on it], and give it a good clean, or replace it with a brand new one. While you're at it, take a good look at the air filter, as it could very well be clogged full of unwanted detritus, and may need a good clean, or even replacing.
B&S engines are normally very reliable, regardless of the model # and a tad of TLC now & then, can often make a huge difference on their performance...
Regards,
mice_elf
Last edited by mice_elf; Yesterday at 09:00 PM.