| Mine used to do it all the time, it's a combination of dirty plates and dodgy thrust bearing on the clutch rod apparently.
FWIW I totally agree with Fil, the 748R slipper is perfectly well up to the job in all situations. I only replaced mine because I was fed up with paying out for new plates and baskets every year!
Replacing it out of some imagined need for better performance is just spending money for the sake of it. In most cases a far better performance gain will be found by sorting out the suspension and brakes.
And no, you don't need a slipper clutch!
Jen. | 
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