The GSC moment of inertia probably isn't too high. If you suspect vibration is causing the float needles to unseat resulting in rich running near idle then check that you've got the blade pitch set properly.
Other threads here deal with GSC setup. Just be careful not to overtorque the hubs. Also, a general caution not to try high speed taxi testing in a Kitfox. You'll be on your way to your first ground loop in nothing flat.