Had my first motor problem with my approx 1 year old Yamaha 15hp 4-stroke a few weeks ago and figured I would share the problem and how it was fixed. I am by no means a motor guy, I know very little about this stuff really, but I figure by posting it maybe this info will help someone else down the road.

The symptom went like this...

When you started the motor, no matter if it was warm or not, it would sound rough. With the throttle in the start position, the engine would run for anywhere from 30 seconds to 4 minutes sounding rough. After a while though you would hear it go from a rough sound to a fast smooth idle.

If you waited for this fast/smooth idle, then throttled down to the lowest idle speed before shifting, it would not stall. If you throttled down while it sounded rough though it would stall 9 times out of 10. The problem developed over time but was pretty consistent by the time I took it in.

The solution was to clean the carbuerator. There was apparently some buildup on the carbeurator was causing it to act this way. In my case, it was covered under warranty and repaired no problem, but if it happened to you, you could probably fix it yourself with some carbeurator cleaner. Assuming of course you know where the carbuerator is and how to get to it :) So that's not complete info on how to fix it but it might help someone somewhere down the line.

I wonder if it would of helped to put fuel stabilizer in your gas. The place that sold me my Honda 4 stroke recommended that I disconnect the fuel line after running the boat and run all the gas out of the carb to prevent it gumming up. The manual doesn't suggest this and I take the boat out quite often and it's a pain to sit there and wait on the trailer with the motor in the water for it to run out of gas. If someone's waiting for the ramp you can't just sit there either. I've added fuel stabilizer to the gas and hope that will prevent any problems.

you probably have some crap in the bottom of the gas tank that is getting picked up. Run an in line fuel filter (in addition to the stock one) and that should keep things clean. Fuel stabizer is good if you plan on having the motor sit for extended periods of time with out use. Gas will turn into a varnish like solution when it sits for too long and gum everyhing up. Unfortunately draining the carb completely out of gas doesn't always get it all out. Gas can get stuck in small ports and metering rods.

I'll look into that. I was kind of surprised that this happened honestly. I run the boat regularly, my fuel almost never sits for more than a few weeks. The gas can was purchased new and I've looked in the tank several times in the last year and never seen anything in the fuel. I'm careful when I fill the tank not to get anything get in either.

But such is life when you own a boat. The minute you buy anything, it's only a matter of time until it breaks.

I will say this... I bought my old 5hp Honda 4-stroke used in 1998 and ran it until 2005, and the only thing I ever did was change the oil once. And it still ran fine the day I sold it. That was one kick ass piece of equipment :)

I have a brand new 2006 30hp honda that had the same problem last september. The culprit-bad gas. It had been two weeks since i was out and i did not run the gas out of it. Started right up but acted rough esp at idle. Took it in and the shop said that water was in the carbs from bad gas and to always run the motor out of gas if i wasn't going to be using it the next day. No problems since but i also do not buy gas from the place where i had the problem (gas station/car wash....hmmmmmmmm...wonder were the water came from).

I have a 20 year old 15 hp. Evinrude 2 stroke on my 14 ft. Valco. When we first got it, we couldn't figure out what the problem was. It started out rough and smoky as hell the first couple of trips out. Found out the last owner, who had only used the boat and motor maybe a half-dozen times over 20 years, hadn't bothered to completely read the directions. He told me to use 100-1 mix oil for the gas BUT the manual says use 50-1 after 48 hour break in peroid! So I changed the oil and mix and now the motor is real clean(for a 2-stroke:(

You know, I've never had problems to carburetors or all that other sh-t bcz I ALWAYS disconnect the fueal line to the tank and run out the gas left in the motor. Usually i'll do this while I'm unloaing my stuff out the boat at the dock. Tie up the boat before i leave and then go get the car and trailer ready. Usaully gettin' rid of all the gas left takes a couple minutes, so I also usually have time to get my rods and boxes out before I pull the boat out. It works for me.