New Mower blowing smoke and oil

Hi, I just bought a mower this summer. It's a Brute 725EX with a 7.25 hp 190cc Briggs and Stratton motor on it. Have used it maybe a dozen times this year and today when I started it up white smoke poured out of the exhaust. I let it cool down and took the "muffler" off and everything "looks fine" but now I am not sure what the problem could be on a new mower. Of course now that I have the muffler off, there is a governor-type of apparatus that was attached on the back side and I am having trouble finding detailed pictures to try to get it back together properly. Any suggestions????

 

Is the engine over filled with oil? Did you have it tilted? The device on the back of the muffler is the automatic choke opener. When it heats up, it allows the choke to open.