I've got a 1991 9.9hp Yamaha high thrust 4-stroke, electric start. I use it as a kicker motor on my 19ft boat.

I like the 4-strokes. My experience has been that they are quiet, fuel efficient, and generally start and run well.

Again, in my experience, the one drawback of this particular 4-stroke (and they very well could have changed the design between 1991 and now) is that the carb jets are extremely small. This means it's fuel efficient, but it also means that any little piece (and I mean LITTLE, the jet holes are smaller in diameter than a thin sewing pin) of debris in your fuel can make the motor run bad, and then you have to pull the carb apart to clean it. They can also get gummed up if you let the fuel in your carb evaporate. We've all heard that your gas can evaporate or "varnish" in your motor, I asked my local boat mechanic how long it takes, thinking he would say a couple of weeks, he said "one hot afternoon would do it"

So now, I use OMC fuel additive religiously; I have a spin-on OMC water separator, plus and in-line filter, plus the Yamaha inline filter ($11 per and it's a little tiny thing under the motor cowling) installed on my boat. Also, at the advice of my mechanic, now when I bring the boat home, I flush out the motors with fresh water and Salt Away, then I pull the gas line off the Yamaha and keep in running at idle. I let it run entirely out of gas. You'd be surprised, at idle, it runs probably about three minutes or more after I've pulled the gas line off. This gets rid of all that extra gas that would stay in the carberator and evaporate and leave goo in there.

Another thing my mechanic told me about kicker motors that I didn't know is that the worst thing you can do to them is run that at an idle all the time. (exactly what we do when we're trolling) It fouls the plugs, fouls the exhaust tubes, and is generally bad for the motor. He said you're better off going with a smaller motor that you run at a faster RPM, or if you stick with the same motor, get a flatter pitch prop so the motor runs at a higher RPM. He said they'd actually last longer this way. He said it's always good to rev them up every once in a while and get the carbon buildup out of there.

-N.