MC500S with engine smoke

I have a MC500S push lawnmower with a Briggs and Stratton engine. I cleaned out the carburetor 2 mths ago and it was running fine. Now, it's smoking from the engine and the lawnmower takes a while shut down even when you release the handle. The lawnmower started to stall yesterday. Any suggestions what causing it to smoke from the engine when shutting down and why it's not shutting down. Any tutorial link would be great. Thank you