| | Yamaha 150 4 stroke "vibration" at 800-900 rpm
Twin 4 stroke 150s, 2006., 97 hrs. When I go into gear and creep forward at 800-900 rpm, port motor has almost a valve knock sound. Slight increase in forward speed, it goes away. If I put it in reverse, then back into forward, it usually goes away too, for a while. Sounds like something is loose, vibrating at a very low rpm. I checked the rudder zinc, seemed tight, wondered if you had any ideas., maybe some simple things I can try to troubleshoot myself.