I have a lt 1554 cub cadet that started running rough. changed plugs, filters, adjusted valves drained fuel, cleaned carb., what else? I ran a compression test it was good. it also has a noise with it coming from engine. not so much as engine bearing or rod noise just a vibration style noise in it. any help appreciated. coils are firing good, but can they still be bad. also there is a ignition advance control on here can that be bad?