Hi guys can I throw out some thoughts here . @rustyc you mentioned replacing the blade . When you did this did you put the mower on it side or upside down ,If so the oil in the filter is come back through the carb . Replace the filter clean the carb and replace the spark plug . You may also want to replace the fuel in the tank as there have been cases where the oil has made its way back into the tank and now your running fuel with oil . @ mayer has a very good answer here and does have a point about the blueish white smoke not being fine. @darkethereal the only case this is fine is if the engine is a two stroke running a fuel oil mix . So in a way you could be right but in the case of a four stroke, which this one is if it has a crankcase full of oil, its not a good thing . You also may have put the wrong grade of oil in the engine . Rusty when you replace the blade did you have to use a hammer or beat on the blade at all . any kind of side pressure can cause a flexing of the shaft and break seals in the crank causing oil leaks . Richard covered pretty much everything else in his answer. One last thing about the run on , a fresh spark plug will probably fix this as the plug is probably fouled and causing the engine to diesel on shut down . So in recap Change out the air filter or clean it if its washable . Make sure you get all the oil out , next clean the carb , and finally replace the spark plug . If after doing all this you have no joy then you will likely need to look at a head gasket repair . wouldnt hurt to do a compression test. Hope this helps