I have a 28cc Ryobi with a flywheel I cut the fins off with a hacksaw. And balanced it with a prop balancer! Since then I have done 2 other engines! From the factory they all most perfectly balanced! I checked this off of another engine! My prop balancer is a frame work of yardsticks. With two aluminum plate’s ca to the top! And a Dubro prop balancer. The one you hold between your fingers. No heavy sides! Also check to make sure the prop is centered! And the prop hub is square to the flywheel! Check the prophub! make sure it’s not out of balance. And remember it’s a 2 stroke single cylinder it will idle rough this is my Ryobi conversion http://www.youtube.com/watch?v=6J7dG...e=channel_page If not you might have a bad bearing inside your engine. check it!