My Honda Rebel sputters when I pump the throttle while idling. I know it has something to do with the carburator because I actually have two rebels and tried swapping the carbs and the problem followed the swap. If I try to ride it, it runs as if it's cold even though it's been warmed up. I tried adjusting the air fuel adjustment screw but it didn't seem to help. Any ideas what could be the problem. Thanks!