Unsure on Zuma's but my 94 Razz will do 30+ consistantly and 35+ downhill. I think it has been tweeked some, but the BB kits do not help I am told. I can get a 65cc kit on Ebay for $72 shipped, new piston, rings, head, gaskets. Then a free flow exhaust for $100.
I am not bothering with it and just ride mine to work and got 78mpg last tank. Next season it will get the **** ridden out of it and well worth the $100 I paid for it and will have another $100 into parts and tags before spring I am sure. It needs tires, brakes, battery yet.