Mine never was stock, though Ive heard good things. I dont understand 3.5hp given that its a magnum top end with a 17 Bing and maybe a differnt piston, plus the stock pipe is a fat pancake at the end of a small header... Mine has always has been just okay, the motor was super trashed when I got it. First I had a 70cc kstar with the stock exhaust for a while, then I made the Estoril fit on it, shortly after it blew the crank. Fixed it traded it, bought it back.
Now I have a polini in it, which I will probably take off this spring and be going to the 74cc eurokit.