Riding lawnmower issues

[deerplanter]

When the engine misses like that it sometimes backfires into the engine casing and creates the smoke you saw in the dipstick. That could overpressure the casing gasket and cause oil leakage to the outside or into the cylinder and foul your plug. I would replace the plug and check any casing vent to make sure it's not plugged kind of like a PCV on your car.

[stykshooter]

My Husqvarna had a similar problem turned out the gas line would collapse use of unleaded fuel makes gas lines soft. Replaced line from fuel pump to gas tank runs perfect again

[Bowtech38]

Looks like the governor shaft seal is leaking

[kruppa24]

Blown sump gasket??? Bad rings/blow by, blew it out. Caused oil leak.

This is possible