John Deere LT160 Lawn Mower?

Mower is 10 yrs. old. Running fine until 2 weeks ago. I detected a slight skip while mowing. The next time mowing, the engine began skipping and choked off. Puff of blueish white smoke from muffler. I have installed new plug, fuel filter and battery. Now when I crank it runs fine for about a minute and then begins to choke down again. Right before it chokes down it runs really rough and starts smoking. Any help with this will be greatly appretiated.