1999 merc. 40 hp 4 stroke problems

npauls · #1 05-23-2011, 02:25 AM

Hey guys/gals

I have been having problems with my boat motor lately and thought maybe I could get some advise on here in what to look at trying to fix first. I don't really have any extra coin due to a back injury and being on disability so I am trying to see if I can fix it myself first. I doubt I will be able to so I will probably end up taking it in to a marine shop but it may be something easy that I have overlooked.

Tonight was the 3rd trip of the season in the boat. The first trip was just to make sure everything was running good but I only launched it in a lake with a 10km speed limit so I didn't open it up at all. The 2nd trip of the season was on the walleye opener at chin lake with my old man and it started up 2nd try without any problems at all. We took a run down to the east end and hit the highest speed I have seen in this boat since owning it without any problems at all. When I decided to go check out another spot after being anchored for an hour or so I noticed that my motor would get up to about half the speed that I normally can get it to and would cut out and start chugging. It was still spitting water fine and the gas line was free and clear with no kinks or anything in it. So when I got home I decided to put fresh gas, a can of sea foam, and new plugs in it.

I launched it tonight at keho for the 3rd trip of the year with a buddy and had a bit harder time starting it tonight but it only took 4-5 times and it was running good. We took a rip out northwest of the launch and shut it down to do a bit of lindy rigging around a drop out while back trolling. After not having alot of luck there we decided to go check the inlet canal for a bit. Well the same thing happened tonight as the other night at chin. We would get to about half speed and it would start cutting out and chugging so I checked the gas line again and it was fine. I shut the motor down and let it sit for a minute and started it back up. We got on plane and up to full speed in no time but while running to the inlet canal it started chugging at full speed. After back trolling around the inlet for awhile we decided we would see how the boat did running to the other end of the lake at the outlet and it chugged going full speed all the way down the lake. I shut it down again and backtrolled around the outlet for awhile and then decided to fire up the main motor and troll some cranks for some snot rockets for awhile. So we are working our way around the dam area and the motor completely cuts out a few times and then when we get it running and keep it running we noticed that the water isn't spraying so good out of the back anymore. I decided to put it in neutral to see what would happen and it would spit a good stream for a bit and then not so good for a few seconds. Then hit the neutral button and revd the motor up a bit and it would spray perfect the whole time the revs were up. But as soon as we started trolling cranks again it would sputter and shut off or have barely any water spray out.

Sorry for the long story but I wanted people to know exactly what I have had happening and was wondering if anyone has any idea what this could be and if it may be an easy fix or if I will have to take it to a marine shop and pay some big coin to get it fixed up?

Thanks in advance for any help.

Nate

Mulestalker · #2 05-23-2011, 03:47 AM

I'm leaning towards power pak, should be able to diagnose with a mulitmeter.
Other things to check would be your gas line,perhaps a pin hole in it,runs fine until it starts sucking hard and draws in air?
-Does it have a tank vent? run it with the cap off to see if it helps?
-time to rebuild the carb/s?

sjb · #3 05-23-2011, 08:11 AM

What about fuel filter has it been changed?

Freedom55 · #4 05-23-2011, 10:30 AM

I have a 2008 4 stroke that was a dog twice for me last year. The first time I took it to the mercury dealer and they changed out a coil. A couple of weeks later I was back with the same problem (sounds like the one you are having) and more than a little p.o.'d with Mercury Marine. Turns out that there was a "maintenance alert" about that very motor so the other two coils were replaced. The problem went away and I still have one one season of warranteed boating with that engine. Try the coils.

Free

Kokanee9 · #5 05-23-2011, 12:47 PM

One thing for sure is get the impeller changed. When you have it apart, run some compressed air through the intake and outlet water tubes to make sure there is no sand or weeds restricting the flow. Whether the problem goes any deeper, as in coils or carburetor, it won't matter much if you crack the head or burn up the pistons and rings from overheating them. Once you have the operating temp where it should be, test the coils or have them tested. Those are the only parts I have ever had fail on a marine motor. It was a merc - 7.5hp one of 2 coils went bad and a used 1 was put on. Ran great after that.

npauls · #6 05-23-2011, 12:50 PM

Does anyone know what an approximate cost would be on coils and impeller? I would just like to know what kind of costs I am getting in to here before taking it in to hopefully have the problem solved.

Thanks,

Nate

Kokanee9 · #7 05-23-2011, 01:24 PM

Quote:

Originally Posted by npauls

Does anyone know what an approximate cost would be on coils and impeller? I would just like to know what kind of costs I am getting in to here before taking it in to hopefully have the problem solved.

Thanks,

Nate

Call up the merc dealer near you for part prices. You should be able to do the impeller yourself, no specialized tools are required. Try to find a used coil, as there is not really a difference between new or used. Just one of those things that either work or don't work. Not sure what the motor looks like under the cover, but if it is a coil, you should be able to do that your self. From what I remember there was only a couple bolts, a spark plug wire, and a little wiring harness that had to be touched in order to change it. The one I had was a 2 cylinder, with 2 coils. you may have 1 coil for each cylinder also. If it is a coil, just have to figure out which one. Send me something so I can send a pdf to you on how to test the coils.

Freedom55 · #8 05-23-2011, 03:53 PM

You will regret the decision to put a used electrics on your engine.

Likely close to $125 a piece and the labour to put them on. Take the old ones to your local Mercury Marine depot and get them tested. Talk to the technician about it. Take the new ones home and put them on. If your impeller is the problem, your engine is probably seized already, and you would know.

Owning a boat is an expensive thing, but if you are counting on it to get you home,or to shore in advance of a storm, or back to the weigh station before it closes, then you absolutely need turn-key reliability.

Free.

npauls · #9 05-23-2011, 04:52 PM

I need to make friends with someone who knows about outboards and can fix them. Maybe I can buy the parts and beer and get someone to fix it up for me.

Looks like this could be a pricey fix like I first thought it may be.

iliketrout · #10 05-23-2011, 05:36 PM

See if you can buy the original dealer maintenance manual. Couldn't get the original for mine but I bought the Seloc manual and it's still pretty good. It would have step by step instructions on coil replacement. eBay should have them.

Also check out the iboats forum. Lots of good advice on there. You could re-post your question there and see what you get but I agree that it sounds like a coil.