I have a 1996 xr600r with a 654cc big bore kit and stock carb. I just bought it last week and the guy I bought it from said it needed a bigger carb(he suggested one from a CRF450) to run right. Right now for it to run without giving constant throttle, the idle has to be way up. Otherwise it coughs and backfires and dies. Once im giving it gas it runs fine though, which is why I'm skeptical about it needing a bigger carb. I'm new with bikes so what do you guys think?