Small Engines (Lawn Mowers, etc.): Yardman 6.5 hp self propelled, air filter assembly, crankcase pressure

Question
I have tried to be very careful with this machine but recently when I started it, it
began to spew black smoke. What did I do wrong? If I put in the "wrong" type of
oil is it too late to clear it out and start again? Thanks

Answer
It sounds as though you are getting positive crankcase pressure this causes the engine to pump the oil up through the crankcase breather and in through the the air filter assembly.  Positive crankcase pressure is cause by an air leak in the crankcase look at the oil filled to and stick O-rings be sure that they are in good condition.  The other way this would happen would be if the mower was to on its side and oil and gas ran into the combustion chamber.  It will take some time for the engine to burn out the oil accumulated in the cylinder so it will smoke for a while.  There will also be a black residue dripping from the muffler.  It has to burn itself out or replace the muffler.  The other thing you should check would be the crankcase breather.  One way to find it would be to follow the little rubber to attaches to the back of the air filter assembly it will go right to the breather.  Remove it if it's full of oil washes out and reinstall using a new gasket.  If this information does not help you out please contact us otherwise good luck on your project.