Briggs & Stratton Van Guard 16 hp D.C. Chipper with Gravity Flow. With fuel switch on and starting engine four minutes, white smoke apprears and increases gradually, then heavier and chokes itself out. Gas is heavy in the cylinders and spark plugs. Also showing up in the oil causing to freeze up. Engine has only 547 hours.

Sounds like your carb is flooding. Inside the carb, there is a simple valve that shuts off the fuel flow when the fuel bowl is full. If this valve fails, or if the float sinks, then too much fuel is forced into the cylinder and will wash past the rings and into the crankcase. This causes the engine to run very rich. You need to remove, clean and overhaul the carb, and change the oil and sparkplug and probably the air filter too. Find the model, type, and code numbers on the engine and go to www.partstree.com , www.ordertree.com , or your local repair shop to get the needed carb overhaul kit. Some B&S engines have an option of carbs, so look for a name on the carb itself...probably Nikki or Walbro. The carb kit is not very difficult to install, but make sure to get everything very clean before reassembly.
Good luck.