My Briggs & Stratton lawn mover puffs out white or black smoke out of muffler in very cold start?

I have a Briggs & Stratton lawn mover 3.75 hp lawn mower and i have a problem. Every time I cold start my mower, it puffs out white, black smoke and smells like burnt oil. Some times it dies when a lot of thick black or white smoke. I started it again and starts out slow then it speeds up when the smoke gets thinner then it stops smoking then it runs fine. I checked the head and its not cracked and the gasket is fine. I saw a lot of oil at the cylinder just sitting there I cleaned it then started it and started fine no smoke. Whats Wrong with my mower? Thanks!