Yamaha banshee idles but wont rev up after changing the stator?

Check wires aren't crushed or exposed. You might want to look at the throttle switches on the carbs and thumb box which are for limiting the RPM with a stuck throttle. You might want to temporarily disconnect the rev limiter box to test for this- just unplug it. Lastly pulloff the flywheel again and recheck the flywheel key.