JD La105 mower problem

I have a John Deere LA105 garden tractor, every once in a while it will start blowing a big cloud of white smoke. When I turn the key to the off position right after, the engine will run for about 10 seconds very roughly then I will hear a loud metal noise then a loud pop and then it will shut off. This started happening after I mowed some tall thick grass (about 7 inches tall).

Why does this occur and how can I fix it?