My lawnmower is spitting either gas or oil from the muffler?

I have a Murray with a Briggs & Stratton 4.0 engine ---push mower. When I went to start it, I had to crank a couple of times on the rope to start it and then I heard some kind of clunking noise and then it started, but smoke started coming out of the muffler along with it spitting either gas or oil...I'm not sure which?
Any suggestions on what it might be and how to fix it?
TL, September 2005
It all depends on if it is oil or gas. Oil could mean rings which is pricey to fix. Gas could mean a carb cleaning is needed which is easy.

cholbach@yahoo.com, September 2005
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