An oldie, but goodie.
Seems the kart has a problem hooking up.
If you're willing to give up ~1 sec in 0-60mph times, theres a more practical solution for what to do with that spare GSXR lump that doesn't have the hooking up problem:
Fun Car's Sportec.
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0-60 in 4.0 seconds and 1.1g on the skidpad is enough to dust 99.9% of the cars out there and ought to hang with sportbikes in the twisties.