It really depends on what you want the cart to do. If it was my cart and I was after more power why not upgrade to a Honda or Briggs V-Twin and be done with it. If your after power you will never be happy with the stock engine.
I changed the rear end gearing. Stock was a 12 to1 ratio and went to a 6 to 1. It is not real fast on the take-off but after about 10 mph it goes good. Top speed about 30 mph with the governor worked on. very well satisfied. I also went to Auto Zone
and got a round filter and worked perfect on the carb.