The black oil coming out of the exhaust (commonly called "spooge") is a common issue with two strokes, but it is best to address the problem and not just try and mess with the pre-mix. Jetting is the most likely cause, followed by saturated silencer packing, worn rings, bad clutch side crank seal, or even a really filthy air filter can mimic rich jetting. However, I would bet on jetting being the most likely cause.
Two strokes, especially small ones, need plenty of top end lubrication. Adding less oil is never a good thing
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