2008 Mariner 40HP runs for a few minutes at high rpm then dies

Hi guys, I am new to the forum and fairly new to engine work, so do not expect me to understand all technical terms. Also English is not my first language.

My engine is a 2008 Mariner 40 HP 2-stroke 2 cylinder (Belgium version) S/N 0P550276. I bought it six months ago and tested it in a barrel and it ran like a dream on the 3rd pull. When I opened the throttle, it would always take a second or two for the engine to catch up and increase rpm. I payed no attention to this. After some weeks' use it began to die immediately when I put it in idle. Since I could always start it again in fast idle, I ignored the problem and just sailed up to the dock at lowest possible rpm and then let it die. Later it came to the point where it would die even in high rpm after a few minutes or less and also be difficult to start again. While I have been gone on vacation, my buddy worked on the engine, and at one point, he could not get it started at all. As it turned out, he swapped around the spark plug caps... Now I am back, and yesterday it ran for the first time in a month. It ran for about 6 minutes at max throttle before rpm went down over a few seconds and it died. I could start it once, run it for 30 seconds at less than max throttle and then I was not able to start it again. Luckily I had stayed close to the dock since I knew it was a risk.

Here is what has been done so far over the course of the last two months:

- Rebuilt water pump with new impeller and gaskets. At one point I had no cooling water coming out, and it turned out my impeller had a broken arm.
- New spark plugs. I probably didn't even need them.
- "New" used CDM modules and terminals for spark plugs. A local amateur mechanic advised my buddy to get these or gave them to him or something. I tested the old ones, they work just fine and their connectors are not corroded as are the "new" ones. I might just switch back to the old ones.
- New primer bulb. The old one was busted.
- Rebuilt fuel pump with new gaskets and diaphragms. The smaller of the two springs and its plastic cap pushing against the diaphragm was missing completely. I do not understand how the pump could work without it. I cannot confirm if my buddy took it apart and forgot to reinstall those parts.
- New fuel hose and bulb for external gas tank.

Yesterday, before I finally got the engine started, I took home the carburetor to clean it. When I got it open, there was not a speck of crap anywhere in it. I assume my buddy cleaned it but I cannot get a hold of him to confirm it. I did not even bother to soak the jet or inspect the needle valve. The float seemed to operate smoothly but I cannot find the correct float height for a WME 98 carb anywhere. Anyone able to help on this?
The idle mixture screw was 3 and 1/2 turns out and the throttle plate was not closed in idle. I set the mixture screw to 1 and 1/2 turns out and closed the throttle plate completely and reinstalled the carb. This setting however, would not allow me to start the engine in idle. I have no choke and no fast idle option, but my throttle lever allows me to increase the throttle without putting the engine in gear. Doing this, I got the engine started. Adjusting only the idle mixture screw would not allow me to decrease the throttle to regular idle, so in the end i opened the throttle plate just enough to allow the engine to run in normal idle. I then ran it at higher rpms (still without putting it in gear) for some minutes. After this warm up, I could close the throttle plate again and leave it idling with no problem. I left the idle mixture screw at 1 and 1/2 turns out.
I then took the boat out for a sail and it went like I described above. After rowing the boat back to the dock (with the wind in the back, thank god) I tried to start the engine again. I was frustrated and forgot that the throttle plate setting was different the last time I tried, so I didn't succeed. However, I noticed that the fuel hose from the fuel pump to the filter was a little too short causing it to bend sharply right at the fitting on the pump. I cut and installed a new piece of hose. By this time I was worn out for the day and when a few pulls on the cord did not start the engine, I went home. When the downpour wears off, I will give it another go. Not sure if it will be today.

Could the bent fuel hose really be the problem if the carb bowl holds enough fuel to run for those 6 minutes? Why is it then only 30 seconds the second time? And why can I not start it after?

I have not tried changing the fuel for fresh. Do you think this could help?

To me it really looks like a fuel supply problem. All my hoses are securely fitted and I do not have any visible fuel leaks. Could I have an air leak somewhere? Maybe a tiny tear in a hose? I have considered to change all hoses - both the small ones for the primer bulb and the ones in the main fuel supply.

Could the fuel tank be the problem? Can I try putting the bare hose straight in the tank or is there a screen filter that I should not bypass?

Would you recommend to go over the carb once more? I would have loved to install new gaskets right away but they will not arrive for another 2 weeks.

Could it be something other than a fuel issue?

Should I avoid running the engine at high rpms without the propeller in gear?

As for the idle mixture screw on the carb: Can you confirm that screwing it in (clockwise) means leaning the mixture and out richening?

I am based in Greenland, which means two things: 1) the ice free summer season is very short and I would really like to get my engine running soon. 2) spare parts are close to impossible to come across locally and take ages to be shipped.
I know I asked a lot of questions. Any help is very much appreciated!

 

To ensure pure fuel flow; you can install a clear glass fuel filter. These are also helpful at eliminating any rust from the tank fouling things.

If the engine won't idle without the throttle open; the carb jets need to be cleaned or replaced or both. Turning up the throttle only empties the float section faster, so the float is not the issue.

You should be able to easily check for good spark on each plug with a visual check before doing the idle jet overhaul.

You should be able to start the engine with the throttle open a bit and then back it down to idle and it runs.

If the engines has a ton of hours and worn rings; you may need a hint of throttle, but this can be achieved with a screw adjustment generally. This might sound like doubletalk, but more like a high hours, abused low oil engine caveat.

 

This sounds like an engine that has had a hard life, already. If you are going to tinker with second hand engines, the first job is to obtain a good workshop manual for the engine, preferably the factory version. Then you turn to the troubleshooting section, and follow the logical steps contained therein. It is amazing how people want to swap out parts etc, on little more than a whim. One of the problems with buying second hand outboards privately, is that often they have been sold because they developed a problem the owner may have tried to "fix", but in failing to do so, had made all sorts of inappropriate adjustments to settings, linkages, etc etc, in the hope they would get lucky. It is simply de rigeur to have that manual, if you want to venture into making your own repairs. Failing that, it needs an outboard mechanic that is familiar with the engine, and that becomes a matter of questionable economics with engines that have limited $ value, and need more than minor work.

 

Thank you for your inputs!

Today I ran the engine for some time. The bent hose had not been the problem. Every time it was about to die, I could keep it running by increasing the throttle a bit more. I guess that completely rules out spark trouble, right?

Is it normal for the propeller to turn very slowly at increased throttle when not in gear and when the boat is not moving?

I cleaned out the tank which had some debris and a little bit of water in it. I also cleaned the fuel filter for debris. That did not solve the problem.

I took home the carburetor for a more thorough inspection.

I realize that my engine probably needs the attention of a mechanic. It was a really good deal though, I would probably have bought the boat without the engine at the same price without hesitation. Fixing it myself would just be a great satisfaction and a great chance to learn something.

 

In this country, there is a colloquialism, "playing up like a second-hand lawnmower", which is used to describe unruly happenings and behaviours, including those of people, in particular, it might just as accurately been, "play up like a second-hand outboard". You really ought to get that workshop manual.

 

Is it the owner's manual or the service manual that I am looking for?

 

Svc

 

Yes, workshop service and repair manual. e-bay might be a possibility, that was a popular engine, one would assume in most cases the manufacturer's manual would be preferred, but others are better than nothing.

 

Just a thought. I think some of the smaller Mariners had a small filter inside the line between the pump and the carb. It really sounds as if you are not getting fuel IN the carb, so recheck everything related. A bad o=ring on your hose connection will cause the engine to suck air instead of fuel, check that too. I think you will find it something simple, and a manual might not help.
B

 

What you say makes since, bruce, but I reckon the manual would have advice about checking those issues. Certainly if you have someone keep the primer bulb squeezed hard while you motor along, and it does not falter, it is pretty conclusive that the problem is between the primer bulb and the carbies.

 

Hi Mr E, actually, in my experience factory manuals rarely are much help on the simple stuff and the aftermarket guides are often too generalized . I do have manuals for both of my current outboards, as well as at least a couple hundred other engine and car manuals, so I do believe in having all info available. However, many do not contain very useful trouble shooting guides, at least for an inexperienced owner. The manuals, factory especially, always have pictures of nice clean parts, suggest using factory shop test equipment, and the bolts are never stuck. Not at all the dirty and salt encrusted engines I have often had to repair. At least it is not in a hot bilge! Since this outboard is in Greenland and resources are limited, I was just trying to help get him back on the water before his season ends.
Several things to try that don't require parts or manuals
It is possible that there are two different problems, like electrical or overheating causing the high speed shutdown and a fuel issue causing the bad idle, but start with the basics. I would try to borrow a known good fuel tank with fresh fuel and as much of the hose system as possible, and install and see what happens. Maybe bypass the external hose connection and clamp the tank's hose directly to the fuel pump inlet. Bad fuel and stopped up filters are always suspect on any engine that has set unused for even a month. Hose and bulb assemblies are particularly prone to crud, and the more you pump them the more crap gets sent to the engine.
Also, make sure that all the pieces of the impeller were found and removed, EVERY one of them. A single piece can stop up the water flow within the engine, cause a localized hot spot and cause the overheat shutdown while water is still flowing out the flow indicator.
Since the engine is "new" to the boat, make sure that the cavitation plate is at or below the bottom of the transom. If it is mounted too high, it is possible that the engine water pickup will starve for water at high speed and cause an overheat shut down.
My latest stopped up carb repair involved finding a tiny hard shelled bug that had gotten in the float bowl on my just purchased 35hp evinrude. It would float free at idle and the engine would run ok, but eventually under higher throttle settings it would lodge in the main jet and shut me down. Then repeat . It took a couple of test runs and a carb removal to find the durn thing. Even then it took a good blast of high pressure air to blow the bug and its parts completely out of the bowl and the main jet. My engine runs fine now, and I suspect the bug was one of the reasons the boat and engine were being sold. I don't mind an occasional challenge, I hate bugs in my engine.
B