Small Engines (Lawn Mowers, etc.): Briggs&Stratton motor problem, briggs stratton, c briggs

Question
Hello, I have a ten year old 12 HP I/C Briggs in a lawn tractor(Murray). I have used it for most of the summer and all of a sudden during a mowing expedition, there was a noticable drop in  power, bluish white smoke started coming from the muffler and got worse as I slowed down and then it just quit. I have since tried the engine and it starts and does the same thing after about thirty seconds. I have noticed that the gas tank is empty and I filled it and it drained over night, I have also since notice I have fuel in the oil?
Is the motor cooked?

Answer
Hard to say whether the motor is permanently damaged but it you have fuel in the oil, the problem is related to either the inlet needle / seat /float assembly in the carburetor or, if equipped, the fuel pump allowing fuel into the engine via the impulse passage.  Check the inlet needle for a wear groove and replace as necessary.  Check that the float isn't saturated (or full of fuel if it's  a brass float) and replace as necessary.  The float assembly should also move freely and be adjusted so the float is parallel to the float bowl mounting flange.  Make sure you also drain all of the contents of the crankcase and replenish with fresh oil once you find the problem.  Hope this helps.