i had the same problem for a while with my variotop too. i tried all kinds of things. different belt widths, weights, even homemade super weights. then i tried bending the springs in and out. but all that did was set the static placement of the motor in a differant place with the same problem.
what was the cure? getting rid of the clutch pulley and adding the stock pulley. sure, i had no idle, BUT, it ripped like never before, variated fully, didnt bang the pulley, gained 5 mph, and alligned perfectly.
small price to pay to have to kick off at a stop. but, just another example of how my clutch pulley was nothing but trouble.