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i'd take it to my lawnmower guy. in case there is oil in your engine. probably not able to happen...but stop the damage from being worse, and just have the pro fix it. that is what i would have said is wrong...you wouldn't believe what He says really happened...i never ever have heard of any of that stuff happening and it happens too me every year. i love my murray briggs and stratton lawn-mower. i'll try to get it rebuilt before i get any other lawn mower.

if you had such a mess with the oil, maybe the head and spark plug needs to be checked for excess oil also. Remove spark plug from engine and then pull the starter a few times. Any excess oil should spray out. Take a wire brush and clean the spark plug then reassemble, try starting. Any excess oil left should burn off, just that it'll smoke for a bit. Depending on which direction(s) the mower had been tipped, the oil could have pooled up here also.

-Mark

I can't figure out how you got oil on your air filter. Anyway...if you got oil on the filter then you probably got oil in the carb. Get some spray carb cleaner and spray the carb before you start the mower and afterit's running. This should solve your problem.