The references to sportbike powered karts reminded me of a fantastic thread that was posted here a few years ago. It gave a great summary, with photos, of several of the ultra-fast Unlimited class Enduro and Road Race karts that appeared at the annual WKA Daytona Kartweek event, held at the end of 2018.
Along with several single and dual-engined laydown enduro karts, there also featured a kart powered by a Suzuki sportbike motor. Not one of those “Youtube Special” bike-powered contraptions that are only run a few hundred yards on some back road or parking lot. But an actual Superkart, or at least meant to resemble a Superkart, intended to be raced on the high banks of Daytona, or any other road course in America.
That Kartweek at Daytona may have been the last time it ran however. Apparently, there were some major handling issues due to the size of the motor that they were simply unable to overcome. I don’t know if anyone else had attempted to run it after that.
I did manage to find the thread. Well worth looking at to see what some of the Road Racers are capable of: