I would consider that classic symptoms of a flat spot. If the mixture is wrong, feeding MORE of it into the chamber will make the engine "run wronger".
Sure, I feel ya, I just meant this isn't a standard torque flat spot - it definitely has a NEGATIVE slope. i.e. torque curve not plateauing, but actually going down.
2014 Duke 690 (Kev's O2 mod, My own fuel mod, decat, GPR Furore exhaust, hollowed airbox with pod filter)