Hi I just bought a used craftman lawnmower with a 6 3/4 hp B & S engine (not OHV). It start up fine but later when I stop the motor there is quite a bit of blue smoke came out from exhaust before it totally stalled. Restart have some blue smoke too but during the running looks fine. I don't have previous history of this engine. My experience is limited to rebuild some Lawnboy two stroke engine and replace valve seal for my own car. I did put 10w30 oil instead of #30 oil into this engine and already changed too. Do I need to take this engine apart and work on the piston rings or valve area? Thanks ahead.