My 4 stroke, 15hp 2000 Mercury purrs like a kitten till about 4/5th or so speed. When I open it all the way, it keeps running, but sputters and feels like it is slipping. I originally thought the prop was slipping, but I took it off, made sure there wasn't any line bogging it down and made sure the holding nuts were tight.

Any thoughts appreciated. Perhaps I need to clean my carb, I do that a couple times a year. It just feels a bit different than it usually does when my carb is getting clogged, but who knows for sure?

Thanks, Paul