Possible /5 Keihan Limitations.
Had a complete set of Keihan exhaust with /5 type silencers on an R75/5. They looked good and sounded nice and civilised. But they had what appeared to be a smaller opening than a stock /5 muffler would have at the rear. Not a big deal on an R75, but when it became an R100/5 I'm almost certain they were choking up the motor.