if you do not have the DEEP GROOVE race type pulleys you will continue to have the problem...also when you put on the DEEP GROOVE pulley make sure you get a COG belt the sits way down in the pulley groove..once the belt sits down in the groove you should see sides of the pulley coming up above the belt...this will 99% solve your problem.
Keep in mind stock type pulleys and stock fitting type belts were not designed for turning 7500 rpm's.
Brian
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "