@Kathy, plugs look great and glad to hear that full bore is able to help out. Keep us posted since everyone is always asking where to get help with rebuilds.
Do you run the boat hard? Have you considered installing the groupk fuel/air separator? It helps prevent lean conditions since it is essentially a fuel pump that draws out the air. I don't know that this is your problem given this was 1 cylinder but it can always contribute. It also makes starting the boat after sitting a quick turn of the key.
I also have to add that while it is apart, at least clean out the exhaust chamber on that bad engine. I would guarantee that it is not completely clean and not having the proper cooling I suspect has caused many people problems that were never diagnosed correctly... cooling system.
I like the oil pump as long as the oil lines are secured and maintained. With premix you introduce new issues (smoke, having to mix at the right ratio, dirty carb = less oil to engine, )