Mercury 3.5 outboard motor

Thread starter #1
I realize this forum pretty much focuses on the sailboat aspect, but I do have a question to anyone that may have experienced problems with this motor. I bought this outboard motor from the Santa Monica Yacht club which was raising money for a charity. It is a 2006 Mercury 3.5hp four stroke long shaft outboard. This motor is hard to start and will only run for a short time by using full choke. I have done some research on this problem and it does seem to point towards the carburetor. I've cleaned the carb several times, but with no change in results. I'm not that good of a sailor and the marina in Lake Havasu City, AZ is like a zoo most of the time. With this being the prime destination for many college kids during spring break and other holidays. So for me, I think it's important to get away from our marina with the least amount of confusion. Any help is very much appreciated. MARINA.JPG
Wild Bill: What does the gas cap look like on the outboard? My outboard has a black cap that you have to open to add gas but it also has a smaller white top on it that has to be loosened in order to allow air into the tank and thus prevent a vacuum situation from preventing the gas from entering the fuel line. On the few occasions that I have used it I tend to forget to loosen the top cap and I have the same problem that you described, it runs for a few minutes with full choke and then dies. At which point I remember to loosen the top cap and it starts and runs fine.
Thread starter #3
Thanks Steve,
I am a big fan of the black motors, but this one has really got me baffled. I'm told this has come about since the motors are now four stroke and the carburetor has very small jet orifices? Also the motors are built in Japan and are pretty much the same for Mercury, Tahatsu, Nissan. Not sure on that. Yes, I did check that the vent was open, also the fuel shut off was on, although this valve is very unusual when determining valve position. I've been told fuel with Ethanol can be a factor. I've used additives like Seafoam and starting fluid, and again, no help. I've checked the Mercury forum without much help there either. The engine looks to be in new condition and this could have been an engine that was returned to the dealer for the same reason. I'm thinking now that maybe the engine was donated to the Yacht club to be sold for their charity? So I'm still scratching my head? This seemed to be such a good deal at the time, as small long shaft outboard motors are hard to find. DSCN0951.JPG and
What I would do is buy a new carb. Bite the bullet and your problems will be solved. Ethanol gas creates major problems for carbs, especially for engines that do not get used much, like outboards. The orifices in a small carb are as small as a human hair and become clogged with old gas. Get a new carb, use a gas conditioner like Sta-bil in every take of gas, and enjoy blasting away from all the idiot power boaters at the ramp. :)
Thread starter #5
Thanks Eddie,
As it stands now, I'll probably do as you suggested. A new carb is around 200.00 and maybe in the future I can get the old carb cleaned by a proffesional that has a sonic cleaning device. Maybe I'll just wait now until cooler weather and the lake will not be as busy at the marina.
Running only with the choke on could be caused by a vacuum leak. I'm not familiar with that motor but testing for a vacuum leak is a pretty standard procedure.
Thread starter #7
Thanks Sailor Al,
When I first got the motor, I hate to admit it, but it ran fine. I decided to do some preventative maintenance and change the engine oil, lower unit gear oil and clean the fuel tank. It was after this, that the motor failed to run properly and was hard to start. The carb has several rubber hoses connected to the engine. Your suggestion sounds like a good place to start. Most of the hoses have spring loaded wire clips or just have friction connections. Thanks again,
You can clean the carb yourself with a chemical dip purchased from an auto parts store. Read and follow the instructions on the dip. After cleaning with the dip blow out all orifices with compressed air. Also, you may be able to purchase a shop manual for the motor on ebay. It will explain how to clean, rebuild and adjust your carb.
If it is a vacuum leak it could be where the carburetor attaches to the intake or cylinder head. An easy way to find it is to get it started and spray a little wd-40 at all possible leak areas and listen for a change in rpm. Be care full. Wd-40 is flammable. You hit a really hot spot or ignition source and the spray can becomes a flame thrower. I've heard the proper way to do it is with a propane bottle. Sounds more likely that the jet is plugged. Orifice is pretty small. Does it run OK at high throttle settings? Any possibility that what you were cleaning the tank with is now in the carb and you are trying to run it on the cleaner? How did you clean the tank? I've had some luck with fuel system cleaners that you pour in the gas tank if the engine will run at all. Depends on what the blockage is.
Thread starter #10
I'll give your suggestions a try. I've had the carb on and off several times and each time after cleaning it and then using compressed air to blow it out, with no change or improvement. Actually, the tank was pretty clean, but still I emptied the remaining fuel and used carb cleaner in the empty tank and flushed it out. Then used fresh fuel with some seafoam added hoping this would help. After researching several forums on these engines, it seems cleaning the carb is a regular maintenance item. In some cases, it has been recommended to use a sonic type cleaning process. I've checked out Harbor Freight for an inexpensive sonic cleaner, but nothing available there either. Unfortunatley other projects have put the motor on a lower priority. What amazes me, is this carb cost about the same as a four barrel Quadrajet, and is about the same as what you would find on the average lawnmower engine. I'm thinking now I'll go the new carb route and change out all the fuel lines and use better hose clamps where needed. I'm thinking also, that this is not Mercury's best idea. If I were choosing again for a small motor, I might consider Honda or one of the other brands. Thanks again for all the comments.
Thread starter #12
I used a combination of fresh fuel and carb cleaner. I did this a couple times and then used compressed air to dry out any remaining fuel. Then filled the tank with fuel and a little Seafoam.
I was wondering if there is too much carb cleaner in the tank and or fuel line. It would be interesting to see what it would do with just fresh fuel in it or if you could get it started and just let it run a while. I'm not familiar with that motor but typically there is a low speed or mixture screw you can adjust. Try richeming the mixture but pay attention to where you are starting from.
Thread starter #14
The type of carb cleaner I used, was in a spray can and used for carbs and fuel injection induction systems. I didn't add that much to the fuel. At times, I could get the engine to run with partial chock and by increasing the throttle, but it would not idle and some times increase in RPM to the point I would have to shut it off. I didn't want to over rev the engine. When cleaning the carb I have removed all the jets several times and also noting the settings. I could probably take the engine to a marine repair shop, but for a simple engine, I would like to repair it myself and know that I could fix it should I ever need too. Again thanks........