Not burnig fuel/runs rough

[Mudslide]

I have a 1998 Mercury 25EH #06597261. I bought it at a state surplus auction two years ago and it was a game and fish motor. It looked new with no scratches or anything. Even the factory paint was still on the skeg. It was missing the prop and starter. I still don't have a starter. It looked like they just used it for parts.

The problems:
1. It runs rough and always has.
2. It obviously is not burning all the fuel. Smokes heavily and I can smell the unburned fuel
3. It doesn't pump a steady stream of water through the pump.
4. It has a sludge/oil mix coming out around the prop. I'm assuming unburned fuel.

I have done a lot to it, so it may be hard to diagnose. Nothing I have done has made any change in performance.
1. New plugs. I also checked for a good spark.
2. Rebuilt the carb with no change at all. I have rebuilt carbs on many machines and never had any problems.
3. Cleaned the connections and every wire.
4. Replaced the impeller. I installed it turning clockwise and checked every wing. No change.
5. The pms screw is turned out 1/2 turn like I got it. That is the only way it will run, unless fully closed.

This is my fourth outboard and none have acted like this. I only use ethanol free gas and use Seafoam every tank. I have tried evertthing I know to do. Mix is 50:1. I really don't know much about 2 strokes. Could it have got too hot and warped something? Thanks in advance.

 

[Mudslide]

Re: Not burnig fuel/runs rough

I just checked the compression. With 10 pulls on each cylinder. Top cylinder 110psi, bottom 110psi.
I ran the plugs about 10 min. The top one was black and wet, the bottom was perfectly clean and dry.

 

[miichael18]

Re: Not burnig fuel/runs rough

does it have 2 carbs?

 

[Mudslide]

Re: Not burnig fuel/runs rough

Only one. A very simple one.

 

[Mudslide]

Re: Not burnig fuel/runs rough

I thought I'd try something different. I took the muffs off and put it in a tub. The pump is working, but its pumping water out of a weep hole in the front edge of the lower unit. Powerhead gasket maybe? Its driving me nuts.

 

[Mudslide]

Re: Not burnig fuel/runs rough

I found part of my problem. The thermostat was stuck (I didn't know it had one)so I just removed it temporarily. Now there is plenty of water coming out of the pee hole. But, it still seems like I have a problem. It's still pumping a lot of water out of every hole in the lower unit. Is it suppose to do that?

And a correction on the flooded cylinder. Its the lower one. The top one is clean and dry.

 

[Silvertip]

Re: Not burnig fuel/runs rough

If one cylinder is black/wet it is fouled. You said you checked for spark but how did you do that. It would appear you have a cylinder not firing. If one cylinder is making power and the other not, it can't be the carb because you only have one. So pursue the spark issue and ignore the water issue. Lower units spew water out of gaps and holes in the lower unit. As long as the telltale is working its ok..

 

[Mudslide]

Re: Not burnig fuel/runs rough

I used one of these. http://www.harborfreight.com/inline-ignition-spark-checker-4424.html

I also removed the plugs fom the engine and put the back in the wires and layed them against the block for ground. Good spark both ways.

 

[will941s]

Re: Not burnig fuel/runs rough

The motor is always going to idle rough.....thats it's nature (it's all the power just waiting to be let go...ha), the tale tale is'nt going to pee all the time at idle with the t-stat in (needs a t-stat) beacause the tale tale works directly off the t-stat. When it opens it pees, when it closes it does'nt. Verify the spark with a tester ans check for a 1/4" strong spark. If it has that then change the plugs (has to be NGK) and try it. Have you ran it yet on the open water? Should be a very powerful motor. How does it run at WOT? 110 psi is a little low (may be your tester though) but it's even, thats all thats important. Have you reset the carb?

Back it in the water and leave the boat on the trailer (tied down), set the idle screw lightly, then back it off 1 1/4 turn. Start the motor. If it don't start keep backing it off about a 1/16'' of a turn til it does.

With it started, put it in gear...just in gear. Back off the screw (rich) about 1/16'' at a time til it begins to run rough. Then tighten it (lean) about 1/16'' a turn til it begins run rough. back it off (rich) about a 1/8 to a 1/4 til it evens out, then about a 1/16 or 1/8 more on the rich side. At that time it should be holding a idle in gear with a load, then idle when it's out of gear. Put it in gear and go to WOT to see if it's making the transition to the highspeed jet (about 1,200 RPM's), then let off to make sure it transitions back to the low speed jet (which you just adjusted). If it keeps running through all the test, you have it set right.

Try this and keep us posted, after the test recheck the plugs also and let us know what you find.

 

[jeffersondodson561]

Re: Not burnig fuel/runs rough

You may want to pull the carb and inspect the reed valve to the cylinder that is not firing. On two strokes each cylinder is sealed versus 4 strokes that are vented to the atmosphere. If your reed valves are ok (meaning not visibly damage; their is a spec for checking them burt they have to be removed) you may have a labryth seal not sealing or the piston skirt for that cylinder may be damaged, this part of the piston is responsible for transferring the fuel air mixture for secondary compression. Although secondary compression is good primary compression may be bad, unfortunately their is no spec/way of getting accurate primary compression. Enough damage to the piston skirt is rare but have seen it, and the only way to determine if it is damaged is to tear down, but this should be done only after all other possiblities have been verified. But check the reed valves behind the carb first.

 

[Mudslide]

Re: Not burnig fuel/runs rough

will941s, when I say rough, I mean it bounces all over the place. I have to keep a firm grip on the tiller. The plugs were only 10 minutes old when I checked them visually. On the water, at 1/2 throttle it still shakes more than it should. At WOT that thing screams.

jeffersondodson561, I will check the reed valves next. If compression is low I would think it would still run better than this if both cylinders are the same psi.

I obviously has a miss. I'm thinking due to too much fuel. Now to figure out why. I suspect it had this problem since it was new. Thanks guys!

 

[will941s]

Re: Not burnig fuel/runs rough

Gotcha....I agree with the reed inspection. If you remove the carb, get a flashlight and look at the reeds, they should be sitting flat against the reed block. Check for cracks and chips, or bent petals. It's just one reed block....one side of the reeds feeds one cylinder and the other side feeds the other one, just that simple. I read in my manual once where it said rough idle could be caused by a failing switch box. Being that it runs like a bat out of hell at WOT, means at some point it is firing just fine, at WOT. Could be the idle side is having trouble, (switchbox maybe) or your having a issue with your idle jet. Maybe theres something stuck behind the needle, or the tip is deformed or not sealing. All the passages in the carb have to cleaned very well with carb cleaner and lots of compressed air. Also, check the vacuum hoses that run from the bottom of the intake manifold (under the carb) to the cylinders. Make sure they are not clogged, cracked, or the check valves are opening and closing on them. That could have something to do with it too. It should two very small hoses that are black with yellow lines on them.

 

[Mudslide]

Re: Not burnig fuel/runs rough

OK, I checked the reed valves and everything looked to be ok. While I had the carb off, I tore it down and cleaned it again. It runs much better now. Not perfect, but acceptable. The only thing I changed was the float. I know I installed it the same way the first time because I marked it when I took it apart. I turned it over because the two sides are different, and it seems to have helped. The valve may not have been closing before. I'll take it out and run it and tune it in the first chance I get. Thanks for all your help. If I have any more problem you know I'll be back!