I have a 15.5 briggs& stratton engine that is 12 years old. Has always ran great,
But now when I start it, it runs real smooth, but it smokes real bad. Any helpful
Ideas would be greatly appreciated.

This is a common problem on B&S engines. Typically, you need to remove and scrape the carbon from the head, piston, and valves every 100 hours. The Teflon coated head gasket is usually reuseable--tighten head bolts 140 in.-lbs.