"Harry K" wrote:

2-cycle oil is meant to be blended with gas (in most cases) and is not
designed to be poured into a crankcase.

True.

My guess is that some serious
damage has been done to the motor.

Maybe, maybe not. The biggest problem is that 4 cycle oil has anti foaming
agents and suspension agents in it, whereas 2 cycle has very little additives so
that it will burn cleaner. The lack of anti foaming agents is probably what
caused the mess.

The damage done will depend on how much 2 cycle oil was added and how long it
was run.

Drain the motor, clean it up, replace the oil with the correct grade, replace
the spark plug/air filter and see what happens...