In the late 80's my uncle up in Rockhampton was building 'hotty' Victa motors for the go-karts he was knocking up. He had an early 125 with no less than 7 carbs hanging from the cases off fabricated manifolds ala radial type placement, he'd cut the piston skirt, filled the domes with resin and ported the barrel as far as practically possible. It revved to 18000rpm on his bench. The local TAFE guys got word of it and managed to do a deal with him whereby they modified it further. 22000rpm they had before it all went bang!
true story
My uncle incidently had to stop building the karts, seems the local police were fed up with a spate of stolen lawnmowers