It is the same with any type of energy flow... it will always take the path of least resistance. Water, air, electricity, they're all lazy... Also consider that what is making the tip black are the carbon particles that are in the exhaust stream. These particles are larger than probably anything else in the stream, and are going to be persuaded to follow the greatest amount of force applied to them...in this case it is the exhaust gas that flows through the left tip...
I just get on mine with a rag frequently and it looks good.
Today
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