I have a craftsman mower with a briggs stratton engine... while mowing last week I ran the mower on an incline (small hill) the mower smoked briefly but continued to run... then when I shut it off to empty the bag, it would not start back up!. I removed the plug (which was fouled with oil) and replaced it... it turned over just fine (key start) but still will not start up... what is possibly wrong?

Hi,
Well, it would be better to have a bit more info, but did you check the oil level to see if it had become overfull from gas? Check the air filter for clogging or contamination, if it gets wet from oil or gas, it is ruined. Newer Briggs have automatic chokes. You should be able to see if it closed when the air filter is off.
Peace,
Clarke