The slow process to become a shade tree boat mechanic.
The boat has issues and it has been brought up in a couple of posts, here and here. The first issue the engine not idling properly and having generally poor performance. The second is the oil dripping out of the lower, indicating bad oil seals.
The engine on the boat is a Mercury 1150, inline 6 cylinder 115 shaft horsepower 2-stroke. I’ve been researching this engine, and it was made from the mid 1960’s to the late 80’s. Mine is a 1988, which I think is the last year of production. It has distributor-less ignition, with a coil pack for each cylinder. It has three carburetors, one for each two cylinders.
What I understand is that, at the time, this was the best performing motor in it’s class. It is also the motor that requires the most maintenance and adjustment to keep it running at that level. The other motors, notably from OMC (Evinrude and Johnson), are more reliable and require less hands-on time to keep on the water. To be honest, I wish this was an OMC.
I had purchased a portable endoscope from ThinkGeek a year or so ago, so this was a good opportunity to use it to peer into the cylinders to see if there are any major issues in there. If a cylinder is in bad shape, it raises the costs substantially to get the power head in good order. I could buy another used boat motor for the cost of getting this one honed and rebuilt.
Anyway, let’s take a look inside.
Most of the cylinders have a mix of carbon and rust on the walls, but no scratches. The piston heads do have spots of carbon build-up, especially the top four. The bottom two are very shiny, so I’m thinking it is either tuned perfectly, or perhaps running a little lean on fuel. Every piston head near the exhaust port is shiny metal. This part of the piston gets very hot, so that makes sense. The carbon will burn off.
I think I’ll need to do a carbon flush on it. Hopefully that will clean the cylinder walls, and loosen any stuck rings. This will provide a much better seal and better performance. I’ve posted before about how this thing has about 80 psi average compression, when it really should be up about 110 psi or more.
The most common method to de-carbon a 2-stroke engine is to use a solvent along with the normal oil/fuel mix and to run the engine. I’ve already added some SeaFoam to the tank, so the motor has been using some of it. That may be why some of the pistons already look shiny.
The mix I plan on using is a can of SeaFoam into a gallon of premixed fuel. The procedure is to run the engine for about 15 minutes to get it hot, then let it set for a half hour. Repeat until the gallon of fuel is gone, then let the motor idle for another half hour to burn out the solvent. The neighbors may be unhappy with the noise and smoke.
There is already some carbon flowing out of the motor. I let it idle for about a half hour one day and the cooling water had a ton of soot in it. The grass below the motor was black. This could just be the normal exhaust from a 2-stroke boat motor, but it looked extra carbon black to me.
The oil leak in the lower has been an interesting adventure. I purchased seals for it and got educated via YouTube on the process to replace them. Very important…don’t nick the prop shaft. That’s a $600 part to replace. I’m still working on this, so it will be in an upcoming post. Suffice it to say, I’m frustrated by it, but did not nick the prop shaft.
I’m also looking at tuning the carburetors as I’m pretty sure they are running rich. Well, the top two carbs might be running rich. The bottom one might be lean. Both issues can make the motor not run right. The procedure is to turn the idle mixture screw in until it stops, then back it out a certain number of turns. I’ll have to look up what that is for the blog post when I work on them. Anyway, once the initial setting is done you run the motor, preferably in water to cover the exhaust ports properly. Then turn the set screws a quarter turn open at at time until the motor doesn’t want to idle due to being too rich. Record how many turns this is. Then you turn it a certain number of turns to lean it out from this point. Again, I’ll have to look this up.
Many forums suggest anchoring your boat firmly, and doing these adjustments on the water. This way you can adjust it, pull up anchor, and try it out. Repeat until it runs right. I’m thinking I might just put a garbage can under the motor and do it in the driveway. It should be ok, since I won’t be putting it in gear.
If this adjustment doesn’t do it, then I’ll be looking at rebuilding the carbs. It is common for the float and float valves to fail on these, which will allow too much fuel into the carburetor. The gaskets also get old and dried out. This allows air to seep in, which changes the flow of air through the carb. Every carb has to be rebuilt at some point.
If I have to rebuild them, that might be a project for winter or early next spring. We will see after the next shakedown.
I had to do some of the same work on my Kawi. Actually on every motorcycle I’ve owned. If there are vaccum ports on the carbs a set of vaccum guages are a must. Your right on those floats. I will have to retest my latest adjustment on the expressway. Thursday on my way to work….. Doing 140 for a sustained time…. Made the motor drop to like 5k RPM no matter how far back the throttle was open. This took me to 70MPH and I was in danger of getting ran over. If I had to guess….. I ran the bowels dry. Might have a blockage in the tank. I think o got it blown out however will have to retest. I love your work on this engine, the scope is a good buy.
There are a couple of things that make diagnosing these carbs a little more fun. This engine was originally equipped with an oil injector, so you didn’t have to do a tank pre-mix and it would change the amount of oil depending on rpm. That part was also prone to failure without warning, so a common fix is to delete it and tank mix. The fuel pump assembly also contains/contained the oil system, so it gets tricky with how it functions with part of it disabled and not lubricated. It does have plenty of fuel pressure and flow, but perhaps an air leak or maybe injecting air into the fuel.
There is also a feeble attempt at emissions controls to redirect some of the air flow to recirculate in the carb. Most people delete that as well, and I need to check these to see if that was done, or done properly. If not, there might be an air leak or pressure issue.
This 1988 was the finest example of a 20 year old engine. It has all the bells and whistles, most notably being point and distributor-less. There is a small adjustment to the stator ring to change timing, and unless that moved somehow, it should be ok. It will automatically compensate for rpm to advance or retard timing.
It just occurred to me…this has an electrically actuated choke. You push in the key to work the choke. If that sticks on, that could lead to the horrible issues at the end of the two shakedowns. I’ll have to investigate that.
At first, I didn’t want to work on this motor, as I didn’t want another project. I wanted to buy it, gas it, and fish from it. The focus on fishing. However….I do have a blog about hobbies, and it makes for interesting content. I just wish I could have planned the work better to film it or better document it. YouTube videos are were it is these days. I’ll have to get my director’s hat on for future work.