Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Oil level correct? Not over full? one cylinder or both? Check spark plug for fouling, showing which cylinder. Are valves adjustable? Are they set and not too tight? If all is well with oil level, and valves, I would suspect yu have a head gasket that is leaking and letting oil be sucked into the cylinder.
Did you find the problem?
Neither plug shows to be oily? And oil is not thinned from gas in the oil. Head gasket would be next.
Or , just thinking, locate the vent line from the crankcase, going into the air intake , usually right at the air cleaner, and remove the hose, and see if it is filled with oil. Oil may be coming from crankcase, into the air intake.