I am working in a 2000 sportsmanship 500. I know how to work on them this is just rattling me. It would not run when I got it so I rebuilt the Carb and cleaned everything up and it starts and stays running now. With the air box on it will barley rev up at all. With the air box off it will rev up more than with the air box. It also is spitting out gas out toward the air box and sputtering a lot. I don't understand. It starts up fine and idles just fine it just goes nuts when you rev it. Please help me figure this out.