Sorry but I would say it is worth nothing. It is too old for anyone to want for racing and you can get a hobby kart that is much newer with an engine more appropriate for a hobby kart pretty darn cheap. It is also not nearly old enough to be a vintage kart so no dice there. I just bought a very nice and super clean early 90’s Invader with front brakes and a running yamaha engine for $150.
Unfortunately it would take more than it is worth to restore. Unless you just want to do it for fun, would be better to buy something in better shape for a little more. Lots of cheap karts from the late 90s and early 2000s out there in way better condition.