Hi...a noob here...I just bought a used Craftsman lawn tractor with a 22hp B&S Intek V-twin. It will vibrate kinda severely, then run smoothly, then vibrate again. It seems to have plenty of power with or without vibration. I am at a loss. Getting ready to pull engine off of lawn tractor and tear down. I just pm'd the tractor...did oil & filter change, air filter change & a lot of other stuff. Any ideas?