Ron,
Kawasaki motored go cart sounds dangerous and incredibly fun! I know a person who was trying to put in a 440 lc into a buggy.
A cr500 or Kx500 put out maybe 40 horses. A cr250 put out maybe 30 horses.
Fan cooled 45 horses out of that intruder motor, well... Liquid cooled mayhem with 70 horses. Pushing round tires, I bet you 70hp could hit 150mph. To the salt flats... 130hp on a 400lb frame can get to 185mph but I don't have a relationship with the ramp for the curve possible for lower horsepower. I expect it is like an exponential curve the faster you try to go, you need a lot of hp to get faster.
When you get to the jetting get in touch with me.