The thingamabob holding the clutch onto the shaft looks like a non-standard
thick washer and a “nut with a female hex socket” on the end? No female parts should be on any kart! Just manly male parts!
Liquid Wrench, WD40 and the like should be doused over those parts to assist disassembly. It looks like you cut a screwdriver slot into the end of the female nut socket? Good idea but to exploit this advancement I would suggest using an impact screwdriver on it. Now for the newbs here (maybe not you), this is a thick screwdriver about the size of a C cell battery flashlight, just like Grampa’s. You put the appropriate bit on the end, stick the screwdriver on the fastener and whack the end with a hammer. Use the largest flat blade bit it comes with.
The Liquid Wrench is best used in conjunction with fire from a propane blowtorch. For more heat, use MAPP gas (yellow bottle). High heat expands metal and thus loosens nuts, bolts and screws. Using all these methods may take a while before success comes or it may come apart immediately.
Let us know how it goes.
EDIT: wait, is MAPP gas discontinued? Just get propane with the blow torchy thing on the end. Bonus points if has a trigger igniter.