1967brutus

The black goo is not caused by your oil, but by the fact that a carburettor never produces a "perfect mixture", and that effect is amplified by unequal fuel distribution over the cylinders.
ANY decent 2-stroke oil will leave the exhaust in at worst a slightly darkened condition if the mixture is 100% correct, but that is near impossible to achieve using a carburettor, because the fuel does not have time to FULLY evaporate before reaching the combustion chamber. The presence of fuel in liquid state in the combustion chamber, at commencement of compression is what is causing the blackness. It is extremely hard to achieve 100% evaporation in the intake tract in these tiny engines. It is possible, but that is subject of a different section of this forum.

A bit deeper into it: an engine running lean or rich as we perceive it (judging by throttle response, peak power and sound) is mainly depending on the ratio between air and evaporated fuel, because that ratio determines the ignitability of the mixture. The part of the fuel that is still liquid when the spark comes, does not take part in that ignitability.
So let's assume, the fuel/vapour ratio is "perfect", just as a starting point. That fuel/vapour mix would on its own burn clean, smokeless and without soot formation.
But once the charge is ignited, the fuel present in liquid state, will also take part in the combustion, and immediately the burn turns rich and starts producing smoke and soot.
You won't notice this as "rich" because this part happens AFTER the combustion has started, and how you perceive the engine to run by ear (rich or lean) depends on the ignitability of the fuel/vapour part of the fresh charge.

Now this fuel that is still liquid, ALSO is still in solution with the oil in the fuel. That means that the tiny droplets are a pretty thick fuel/oil mix (maybe 1:1 or worse) and now you have tiny globules of mix, of which the fuel burns off in an increasingly oxygen-deficient environment ("producing soot") and oil which barely takes part in the combustion, BUT this oil due to its cleaning and detergent action, absorbs the soot. Result is blue smoke and black crud.

There is very little you can do about it, it is not in the specific oil you use, it also is not in the fuel/oil ratio: If you would, for example, start using 15:1 instead of 20:1, you would not see a really significant change in the gooeyness, nor the amount. A little bit, but not as much as expected. If you would use 25:1 (mind you, I am NOT advising this) you would see no significant reduction of goo. But you would most defintiely see increased wear and reduced engine life. Meaning, the gooeyness is NOT about "too much oil".

The only thing that would help, is provisions to promote fuel evaporation during transfer from carb to intake valve.
For example a very fine metal screen downstream of the carb. For experimenting and gain of understanding an interesting thing to do, but for practical use probably not very advisable, because fine-mesh screens clog over time, leading to issues that would really ruin your flying day.
Another method would be fuel injection instead of conventional carburation, but while absolutely possible (people have done it), it is not an off the shelf solution and involves a lot of tinkering.

Best is to just accept it. The black goo is nasty but still WAY easier to clean than Castor-goo.