I have Merc 1997 2 stroke 4 cylinder. It's the 2+2 cylinder where it kicks into 4 cylinders around 2500 RPMs. It's seen its fair share of abuse and hours, but it runs just fine and has been very reliable for me. However, I've noticed for the past 2 seasons or so that sometimes when underway, at high speeds or low speeds, there is about 2 seconds of vibration and a different noise pitch, followed by normal smooth operation and sound for the same or longer time. It seems that I hear it on some trips, and not on others. I should also say that the engine has the tell tale higher pitch knocking sound as well, which I'm told is a sign that the engine is on the way out.
Prop has been replaced last season and is in perfect condition, LU oil always changed every season, carbs cleaned last year, spark plugs replaced every season at least, fuel is good, I check it obsessively every 2 weeks for water and crud. Water separator changed regularly.
I'm really wondering if this is somewhat normal, or if I should expect a rod to come flying through the cowling some time soon or the engine to blow up. Anyone have some insight for me?
