My father just boat a 2017 Crestliner Discovery with a 2016 60hp four stroke Mercury. The engine starts up great and runs fine until you go over 5rpms. To describe it best, it stutters. The engine will cut out and then go, then cut out and go a little. It rocks the boat forward then stops and so on, until it eventually is idling. We have to stop and put it in neutral to even go half speed again. We can only go half speed as of now.
We have replaced the gas (no water in the lines) and put C-foam in it, but nothing helps. Just curious what others might think would be the problem on a two year old engine?
Any help or advice is much appreciated.