I can't see that something would go wrong with the HRC card and aftermarket pipes. You must've had other mod.s in it right? Something affecting the airflow/jetting?
I had my MC28 with that spec. and never a problem.

But then what do I know?

Commiserations, I know how it feels.
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MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-