Evinrude 28 SPL Running Rough

Hello all,

This is my first boat/outboard but have worked on cars and small engines for many years.

The boat I purchased was in storage for 10+ years and was sold without the motor but when talking to the gentleman he said the motor was remove because it was locked up from sitting for so long.

I told him that sometimes you can free them up and still use them, he said if I bought the boat he would throw the outboard in so unfortunately I dont have any history on the outboard.

To get to where I am now I filled the cylinders with marvel mystery oil and let it sit, topping it off every few days after 2 weeks tried to break it free and it turned over relatively easy.

Pulled the carb off and cleaned it and installed a rebuild kit, but it was pretty heavily oxidized. I also replaced the water pump.

When I tried to start the motor it started right up with very little fuss, revs, and there have been times when it seems to run pretty smoothly but normally it will run pretty rough and then "fart or sneeze"( I've seen what I think to be happening referred to different things while searching online) and then die normally.

I have checked compression and got 125-126 on each cylinder just to check the health of it.

I've pulled the carbs 3 times assuming that I had missed something but now I'm starting to think there may be an issue elsewhere but I'm not too sure where to start.

One question I do have is that although I rebuilt and cleaned the carbs and checked that all passages were clear I did not remove and replace the soft core plugs, at the time of rebuilding it I had not seen a carb where those were replaced during the rebuild. I can go back and do so if that could be the issue but my thought process was if the passage is clear it shouldn't be an issue. Please let me know if I am mistaken.


Here is a video of it running, granted this is probably the best it has run yet. The only things I have done as far as adjusting is using the screw at the top of the carb.


https://vimeo.com/538815646

*When you hear the idle going up that is me raising the idle lever*
Thank you in advance for any assistance!

Open low speed mixture 1/2 turn and test run.

racerone said:

Open low speed mixture 1/2 turn and test run.

Click to expand...

I tried previously and just tried again to adjust the low speed mixture. I started about 1 1/2 turns out but played with it going higher and lower in small increments to see if it would help/hurt.

while adjusting the mix seems to change the RPM slightly the miss/rough running doesn't seem to be affected.

I also pulled the plugs a few times to see what they looked like and the top cylinder was very wet and black and the bottom cylinder was very black but completely dry.

I cleaned them off a few times and ran the motor again to see if it was consistent and got the same results several times. I swapped the coils and signal wires and same results.

I'm assuming the top cylinder is running much richer than the bottom? or perhaps a dead miss. I'm not too sure how each cylinders mix would be different since there is only one carb.

Please let me know if any additional information, pictures, or videos would help narrow down the issue!

Thank you

Answer the questions.-----Does the primer bulb go hard ?----Do you have spark on both leads that jumps a gap of 7/16" ?----Inspect fuel pump diaphragm ( you say top plug is black / wet ) on your motor.----And post a picture of the stop on that wire rod that goes to the back of the motor.----Picture of the stop at slowest idle.

racerone said:

Answer the questions.-----Does the primer bulb go hard ?----Do you have spark on both leads that jumps a gap of 7/16" ?----Inspect fuel pump diaphragm ( you say top plug is black / wet ) on your motor.----And post a picture of the stop on that wire rod that goes to the back of the motor.----Picture of the stop at slowest idle.

Click to expand...

Ok so

1. the primer bulb does go hard.
2. I can not find my spark tester but am looking for it
3. I took apart the fuel pump and all diaphragms appear to be in good shape, no tears, holes, or excess wear.
4/5. I'm not exactly sure what you mean but I think its one of these two, please let me know it not.(these are both with engine off with the idle set to lowest, I am not sure if you need it when its running.)
https://imgur.com/HxaZOhK
https://imgur.com/cUazO6q

On a side note when you asked about that stop on the rod I started looking around and there doesn't seem to be all that many options to adjust on this motor so I disconnected the linkage from the throttle plate to the "ring" below the flywheel started moving the "ring", which I can only assume adjusts the timing ,and I was able to get it to idle much better for a minute or two before it just went back to the way it was running. (Video of it running better below)

https://vimeo.com/539314409

Thank you again and if any of the pics are incorrect or you would like more/better pictures of anything please let me know!

You need to look into a process of adjusting that stop.----At this time it does not look right to me.----And no I am not going to type out the method I would use to set the linkages on that motor.----Factory manual is in your future.

racerone said:

You need to look into a process of adjusting that stop.----At this time it does not look right to me.----And no I am not going to type out the method I would use to set the linkages on that motor.----Factory manual is in your future.

Click to expand...

No worries I appreciate the help getting this far!

I will begin investigating adjusting the linkages/timing and getting a service manual.

Thank you!

Hey Guys,

So I am still trying to get this issue resolved but I after ruling out a lot of things I think I may be onto the actual issue.

I believe that my issue is indeed a "lean sneeze", if I continue to press the key in every few seconds to prime the carb I can keep the motor running indefinitely and as soon as I stop after about 5 seconds the RPM begin to rise and then it "sneezes" and dies. So I could be wrong but I'm currently working under the assumption that the issue is that the carb is running out of fuel.

I have already rebuilt the fuel pump so I haven't looked into it too much but it is pumping fuel but I'm not too sure how to determine how much fuel is the proper amount.

I've gone through the carb 10+ times and swapped parts back from the original to the rebuild parts and there is still no change.

One question I do have is after putting the carb together I always test the carb but blowing into it and making sure it allows air when its supposed to and stops air when its supposed to, my question is that when it is allowing air how "free flowing" should it be? I can blow air into it but there is definitely some back pressure.

I also found an old post from Joe reeves helping someone with a similar issue and he described a test for the solenoid primer and mine is function properly according to his test though I'm not sure why that would affect the motor running as I thought that was only used for cold start.

Any suggestions or help would be appreciated!

Thank you again.

The electric primer is a valve.----When you push the key in , it opens and the fuel pump then put fuel directly into the airstream through this primer valve.----This fuel bypasses the carburetor and the metering circuits and jets.----This strongly suggests you need to look at your carburetor.

Viper588 said:

One question I do have is that although I rebuilt and cleaned the carbs and checked that all passages were clear I did not remove and replace the soft core plugs

Click to expand...

Those plugs cover passages that are machined during the manufacture process. You need to remove those plugs and ensure everything is 100% clean under there when doing a carb rebuild.

racerone said:

The electric primer is a valve.----When you push the key in , it opens and the fuel pump then put fuel directly into the airstream through this primer valve.----This fuel bypasses the carburetor and the metering circuits and jets.----This strongly suggests you need to look at your carburetor.

Click to expand...

I very much agree with you! But in this case I am telling you this carb is clean, I've had the same thought you just explained several times and soaked the carb, ran wires through each passage, sprayed carb cleaner through each passage, checked where each passage goes and ensure its clear both directions. I've come to the conclusion that I MUST have missed something in the carb so many times that it has been thoroughly gone through multiple times.

I have debated ordering a replacement carb but have been a little hesitant just because of how clean the carb is and I cant see how it is the issue but here we are.

I have also considered bringing it somewhere just to see what they say and determine but I am not in any rush and I do enjoy doing the repairs and learning more about the vehicles I own for the future.

kevinj said:

Those plugs cover passages that are machined during the manufacture process. You need to remove those plugs and ensure everything is 100% clean under there when doing a carb rebuild.

Click to expand...

Hi Kevinj,

Since I posted that and had so much trouble I did go back and remove the soft core plugs and inspect under them about a week ago. Everything looked great under them and was very clean(unfortunately =P).

Thank you for the suggestion!



I have been contemplating dropping the boat in the water and giving it a little bit of an "Italian tune up" to see what happens, even though I'm having issues with the motor its never not started and dont think I would get stranded. The main thing holding me back is that though it seems to run much better at a higher RPM in gear I know running while there is a lean condition can damage the motor.

Thank you again for everyone's suggestions and input!

Good luck with your motor.---I say there is an issue with your carburetor.

Hey guys!

I had some time this weekend and was able to work on the motor a little and found what may be the issue or at least part of my issue.

I seem to have a fairly large vacuum leak. I went around the motor with LPG and found the area where it seemed to be but I couldn't really pin point the spot, I used some brake cleaner as well and again I am having some difficulty identifying where the exact leak is.

The leak is some where at the base of the motor which makes it difficult to see what are is being affected. I did some searching and found a few instances where vacuum leaks at the base of the motor where the drive shaft seals are but they said normally the drive shaft would be blackish/sooty which mine was not.

https://vimeo.com/559754462

Is there a "common" vacuum leak spot at the base of the motor or a method for identifying the leak? I have a smoke machine to test if needed.

Thank you again for any help!