The VSX variates from standard powertorque set ups mostly in regards to the intake.
The air hose is wider, the carburettor has different jetting, the intake manifold mount for the carby is straight, not dog-legged, on top of this, the muffler is an increased flow model.
It is designed to run at slighly higher revs, and overall produce an increased power output.
If the mixture is ritch this can indicate either excess fuel is comming from the jet, or not enough air is getting into the engine.
Due to the increased airflow, this engine can be more sensitive to a dirty air filter, or intake/exaust obstructions.
A rich mixture can cause less rev's and power than the engine is designed to produce, causing a lower temprature, this, combined with the excess fuel can lead to spark plug fouling, oil fouling of the muffler, carbon build up, and further obstruction to the engine.
The first step here is, in my opinion, to focus on the air flow through the engine, check the exaust port, the muffler, the air filter, air hose, carburettor inlet, body and mount, and if neccisary, the intake port, for any sign of obstruction.
Also checking the machine is corectly calibrated at the throttle is important, as it maybe sligly stuck in choke setting.
