That engine is a genuine V-twin, so that rear exhaust pipe should be getting as hot as the front. If it is fake, take the shields/covers off and see if that rear pipe T's into the front. That said, the pipe close to the head should still get hot, even if one of the two mufflers is a fake, which leaves me to think you have a rear jug with low compression or weak spark that is blowing out under load.
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