Have you checked that your spark plug caps aren't loose? This is a common problem and does induce rough running. Just use a dab of loctite on the threads to stop the caps from shaking loose.
Edit - I've just re-read your post and it does sound pretty severe so probably more than just loose plug caps! Having said that, there's no harm in dealing with them anyway.
Last edited by Bunny; 27/08/21 04:19 PM.
