2002-sea-doo-sportster-lt with dual 717s. All works and runs fine except for while idling. It idles nice and low rpm but surges every 10 seconds from 1300 to 2000 rpms for about 3 seconds and then back down. Keeps going like that. When i get going. It doesnt do it. Only while at lowest throttle position.what could be causing this? Carbs need adjusting?