Nauticalwaller
New member
After a 100 hour service my 2009 Yamaha 150 4 stroke "knocks" when at low 600 rpm and in gear. (forward and reverse). It does not knock when in neutral. When I put it in gear it will knock at 600 rpm but goes away at approx 700-800 rpm and above. The certified Yamaha repair shop claims that all Yamaha 4 stroke 150 to 200 hp engines knock at that low rpm range. I've only owned the boat for a few months and noticed the knock just after the service was complete. Does this sound correct or does anyone know why this would be occurring?