See attached, not as curvy as what you had, but maybe it'll work or give you a different method to try.
Still used a 3D sketch for a path, but gave the main curve sketch entity following the pulley/fan an on plane relation to the plane I inserted, and the other path lines have all along x, y, or z axes relations. The second sketch entity attached to the main curve also has perpendicular relation to a surface of the pulley/fan. After I had the arcs and straight line sketch entities set the way I wanted, I used the tools>spline tools>fit splines tool to make a spline out of all the sketch entities. Uncheck the closed loop option, adjust tolerance as needed.
Direct link to helpful hints: http://www.solidsmack.com/solidworks-spline-curvature-control-surfacing/2009-10-13/
Go to this blog and search for 'spline schlime': http://dezignstuff.com/blog/
You could also post a pic of what you're trying to do.
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