Gentlemen, we need to standardize our terminology about richness.
Some keep quoting K&B's description of sloppy rich running. I think
they are off the charts, and not in line with a "real world" examples.

Let me offer my version, in a scale that I have devised. I think it is
pretty accurate in the general sense of two cycle engine operation,
to include the small aero-model engines.
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From lean to rich:

0. Engine not getting enough fuel to run.
1. Engine ran but was set too lean. Overheating and seizure resulted in
engine damage (repairs are needed before engine will operate again)
2. Engine is running, but is slightly lean with some over heating.
3. Engine is running properly, but should be richened for sustained
high speed operation.
4. Engine is slightly rich, will sustain high speed operation.
5. Engine is set rich, and will sustain high speed operation, as well as
extreme load operation.
6. Engine is set overly rich, RPM and power are down somewhat from
peak, excessive smoke from exhaust.
7. Engine is set way too rich, power and RPM are way off peak. Excessive
smoke is seen and engine is cutting out. (breaking into 4-cycle)
8. Engine is set sloppy rich, into a four cycle mode. Engine is no longer
exhibiting two cycle performance, power and RPM have dropped to
where normal flight maneuvers cannot be performed. Raw unburned fuel
is misting out of exhaust on every other revolution, smoke is excessive.
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This is where I draw the line. K&B calls this point "slightly rich".
I disagree with K&B's assessment, or description of rich running.
Trying to define stages of richness past this point is moot, because
not only is power down to the point where flight is becoming unobtainable
the plug is going to drown, and the engine will quit anyway.

Keep in mind that a two cycle engine running wide open can ingest
an astonishing amount of fuel, and keep running. A four cycle motor
cycle engine will not run past the #5 area above. It will cut out and
misfire, just like it has an ignition problem.

If one was to take K&B's silly assessment of engines running in a stage
9 or 10 in my example....how would you "RUIN" an engine that
just died from the plug drowning, and the fire going out ? Who's
going to operate their engine in a ridiculous fashion way past a
four stroke ?

I will state, IMO to say that an engine that is firing every other stroke,
and spitting raw fuel out the exhaust....is running "slightly rich"
is absurd ! [X(]

FBD.