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Engine seems to be running rich

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Billhein94

Member
OK. . I'm going to make a short story long in hopes that somebody can make some sense of what I have been doing.

Earlier this year I bought a 14 foot boat and trailer with an Evinrude 25 HP (ended up being a 1975 25502B). I took it out and it started up just fine. It ran good, but WOT didn't seem like it should. RPM's seemed low and wasn't as much power as I was hoping for. I also notice that it had a hard time idling. . like it would die when I cut the throttle. It would start right up again, but I would have to give it some throttle to keep it running. I also noticed a significant amount of fuel/oil in the water. I took the hood off to look at stuff and when I went to take the spark plugs out, I noticed 2 things. 1: The plugs were dark and wet, 2: the bottom plug was not connected. So....I connected the plug thinking that the fuel in the water was from unburnt fuel from that cylinder. I ran it the rest of the year like that. Still seemed low on RPM's still not as much power and still not idling very well still fuel in the water, but it was manageable.

This fall, I decided to rebuild the carburetor to hopefully clear these issues up (I am not a mechanic and have never done anything like this before) After watching videos and reading forums I felt I had a pretty good grasp and it was also recommended that I rebuild the water pump as well. So I rebuilt the carburetor, with the kit from this site. I did notice that the slow speed needle was out way further than it should be like 5 or 6 turns. Knowing what I know now. . there is a good chance that was the major cause of all my problems. When I put everything back on I also noticed that the butterfly valve for the throttle was not opening all the way at WOT. So, I lined up the cam follower with the end of the biggest lobe (which should be WOT) and adjusted the linkage so the valve was completely horizontal. I do have a service manual, so I followed it to link and sync the throttle with the 2 lines. I also replaced the impeller on the lower gear unit and put in all new fuel lines.

I got it started, but it was running even more rich than before I couldn't even keep it running. There was a lot of fuel in the barrel that I was running it in. It was recommended that I take a look at the fuel pump, so I just went ahead and put in a new one. Things improved with the fuel pump and I was able to start it and keep it running. I was able to make adjustments with the slow speed needle and could hear changes in the engine. I could put it in gear and increase the throttle but it would seem to sputter. I checked the spark, but it was with a cheap tester that just shows a light if there is spark or not. When I checked it I noticed some spark coming from behind the bottom coil, almost like it was sparking to the engine block.

Oh yeah. I have a 1973 18HP that has a lot of compatible parts as well. .. so, I took the a coil from that to fix the spark problem.

So, where I am at now. . I can get it to start pretty easy and it will run, but I am still seeing a lot of fuel in the water and the plugs are still wet and black. I did notice a small pool of fuel at the front of the carburetor (not sure if that is normal) and also when I put the carburetor back in from the rebuild it looks like I might have pinched the vacuum line the is back there. (I'm not sure what that does....fuel pump?) My next step in my head is to change the points and condensers with the thought that I don't have enough spark and unburnt fuel is coming out of the exhaust and showing up in the water. I am hesitant to take off the flywheel because I really don't want to mess with the timing. I was also thinking that the reed valves may be at fault and the 18 HP motor has the same part number. So maybe between the 2 motors I can get one good one! Another thing to note, I have been able to start it without using the choke and that leads me to believe that is still pretty rich.

Also, the idle screw is missing, so I could be going to far and allowing the RPM's to go too low, maybe that is the cause of my idling woe's. I have an RPM indicator on the way and I plan to get that part figured out then I can make other adjustments.

It really didn't run that terrible before I started tinkering and I am afraid I am making it worse, but I don't think I have ruined anything yet?? Am I on the right track here?
 
Did you check the compression? Did you replace the plugs? Running in a barrel it must have cowling off or it will always be rich. I often even supply fresh air with a fan in order to keep the motor from inhaling its own fumes which lack oxygen, further causing it to run rich. Make up a simple spark gap tester and see that the spark can jump a good 3/8 in with both plugs out and a good swift pull on the rope. Where does that tube lead that you pinched when you worked on the carburetor? How many turns out is your low speed mixture screw now? Idle screws are often missing on these and it is not the worst thing that could ever happen because you can stop the motor by simply turning the tiller grip quickly to stop in case of an emergency....like "iceberg ahead"!
 
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So, I have a compression tester on the way and spark is good. The pinched line goes from the bottom of the intake manifold to a point just above the fuel pump. I have been running outside with the cowling off. I followed the service manual and started with the needle valve 1 1/2 turns out and it is probably sitting about 1 full turn out now after adjusting things.
 
So is the little tube injured? Did you try new plugs gapped at between .025 and .030? I run about .028 on my points/mag ignitions. If everything is right, spark should easily jump 3/8" with a sharp blue/white lightning like "snap". I have had best luck with Champion plugs in all my older OMC's. However, I run Amsoil Saber at between 100:1 and 80:1, or Amsoil 100:1 pre-mix at between 64:1 and 80:1, in my older outboards. That's just me, I've only been doing this for 47 years, so maybe it's only "luck", that I have never "toasted" up a motor. Scored a chain saw cylinder, Stihl 041 AV, but I think it was a pre existing condition. Put a new jug/piston on in 1980 and it's "Stihl" running sweet. Use it almost every day in our firewood business. It has always had Amsoil 2 stroke, mixed at 2 oz. Per gallon, (64:1). Anyway, nobody much cares about that, but your 25 horse... evolved from 22 cu. inch, has the greatest power to weight ratio of ANY outboard ever manufactured. I have several of them here. They started at 18 hp but soon evolved to 25 hp. The bore was the same, think they added a little stroke, changing pin position in the pistons. Were both plugs the same color? If the cylinder associated with the fuel pump pulse is/was running richer, then certainly there is a good possibility that the pump diaphragm was/is leaking fuel into that cylinder.
 
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The little tube doesn't appear to be injured it just looks folded over from the carb pushing on it. I will have to take the carb off to straighten it out. Do you happen to know the function of that tube? I know I have spark, I haven't had the chance to check the quality of the spark. I put the NJK equivalent in I think the were B8, but recently cleaned up the original champion ones. I didn't want to put brand new plugs in until I had the fuel system figured out. Both of the plugs seem to look the same. Do you think it is worth pulling the flywheel and changing the points or should I just check the spark and go from there.
 
Pulling the flywheel and maintaining the points is part of owning an older motor.----Should be done as needed.-----If coils are original I recommend a new set.
 
If points are set at 0.020" , or with a meter using the timing marks there in no timing issues to worry about.----Just reassemble with tapers clean and dry.---Torque nut to 45 FT-LBS
 
Fabricate something !----Piece of flat bar steel and drill 2 holes so you can use 2 of the 3 holes 1/4-20NC that are in the flywheel.
 
I do not reed a picture of that cover.----I am assuming it has the ring gear on the flywheel.-----Use a flywheel turning tool.----Note----The shiny cover can be left off.----It is merely decorative.----Your opinion may be different.
 
I got the nut off with some wd40 and some convincing with an impat. There I found the three holes. I have a puller, so the rest should be a piece of cake
 
I got the flywheel off and both the points were gapped at 0.14. I plan to change them along with the condensors. just curious what too small a gap would cause
 
timguy said:
<snip> ... If the cylinder associated with the fuel pump pulse is/was running richer, then certainly there is a good possibility that the pump diaphragm was/is leaking fuel into that cylinder.
Click to expand...

This is happening with my 25R70E right now. I didn't consider that the fuel pump could be dumping fuel into the cylinder. It's smoking like crazy and I have to hold the throttle open to keep it running. The bottom cylinder with the fuel pump is wet and black when I pull it out. Thanks so much for this.
 
Yes this is a sometimes complexing problem. The pump will still work, but that vacuum will scoop up the excess fuel into just one cylinder. I have run into this fairly often....and the owner is ready to scrap the motor. They think it's reeds or carb, get discouraged. Funny, but at high speeds, the symptoms sometimes disappear.
 
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