Spark plug in lawn mower keeps fouling

Question

Wondering if anybody knew why a spark plug in a push lawn mower would keep fouling. Add a new spark plug but after Im done mowing that one is covered black with what appears to be oil or something.

Answer 1

We had the valves adjusted on one side of our twin engine on our craftsman 24hp mower. It is acting up again. The plug is fouled and it cuts out mostly when blade is engaged. Do we need new valves? Please help, we have 2 acres we mow and I don't want it to get ahead of us! thanks