lawnmower keeps fouling plug???

could also be a dirty airfilter which in effect chokes the engine. Is the unit puffing black while running? Does it stop running poorly if you remove the airfilter while it it running? The more info you give us on the problem/question , the better quality answer you will get.
Re-design7 years ago
1. Wrong plug. You need a hotter plug.

2.  Choke stuck, carb out of adjustment.  Getting too much gas.

3.  Weak spark.

4.  Burning oil.  Need new rings.