Hi Murray, the dirty air filter would cause rich mixture, which would normally result in black (petrol) smoke, not blue (oil) smoke. If you had blue smoke, there may have been some old oily deposits in the combustion chamber or the muffler. Running the engine with rich enough mixture to cause petrol smoke may also have caused some cylinder bore wear, since the petrol washes the oil off the bore. I suggest you check that the engine oil is clean and does not smell of petrol.
