I've got a 10hp kicker that was doing sort of the same. Mine sounded as if it was choking out all the time. I would get spurts of power like she wanted to run and it smoked a lot. Seemed like a fuel problem but everything checked good??? Ended up having an air leak that was causing her to run wayyy to rich..

There are a few things that you can do. You might have an air leak that could be coming in from around the carb. You may also have a bad seal, there are three of them. Two on top of the drive shaft and the third, the hard one, is located on top of the crank right under the fly wheel.
So finally I replaced those seals and she ran sweet again. The bottom two seals are generally the ones that will go and not the top one.
Now if you are comfortable will taking the whole lower unit off the two seals can be changed in about an hour. They are located right under the power head where the exhust and drive shaft come out. If you decide to do it yourself just ask whoever you get the parts from for the whole seal kit...Around $30?? That will include the exhaust gasket too.

Good luck..