1998 15 hp - won't idle / clunk noise

[b_arrington]

I have a 1998 Evinrude 15 hp. Model E15RECR, SN G04514576.

Problem
Currently the engine will not idle. It needs a good amount of throttle to stay running. Also at idle, I noticed an intermittent bur frequent "clunk" noise. At the same time as the "clunk" the engine torques to the starboard and the engine speed slows way down. If no throttle is applied, it will stall. It almost seems like one cylinder has misfired and is causing a stall. If the throttle is advanced there seems to be no "clunk". The clunk had been observed 2 seasons ago but went away.

Recent issue history
2 weeks ago the engine stopped running while in use and would not restart. Was diagnosed with a stuck float. After the float was freed the engine was not idling well at all (would die when tiller set to idle speed). High speed performance was fine and normal.

Recent work done
I had messed with the carb / settings for the no start issue, so I installed an OMC rebuilt kit. I used a shop manual to perform the sync / link adjustments post carb installation. I've done all up to the point of setting the idle speed / idle mixture adjustments in the water with a load. I'm waiting on a tachometer to do those.

After installing the carb kit and the doing initial adjustments the engine fired up right away and idled fine for about 5 minutes. I shut down and restarted; this is when it stopped idling and I observed the "clunk" and RPM decrease problem. It was while making adjustments on the stand with water muffs that the "clunk" and no-idle problem started.


The fuel pump is fairly new. The fuel pump screen is clean. Spark plugs were new this season and are the factory spec type. The fuel is fresh.

Thanks for any help with the no idle / clunking issue.

 

[racerone]

Water pump impeller replaced recently ?-------Compression test done ?----You may just need to open the low speed mixture 1/2 turn as a test.

 

[b_arrington]

Water pump impeller replaced recently ?-------Compression test done ?----You may just need to open the low speed mixture 1/2 turn as a test.

Water pump was replaced 2 seasons ago. I get a strong stream from the tell tale.

No compression test done as of yet. I would need to get a tool for that, which I don't have at the moment.

I plan to make the idle speed and idle mixture adjustments soon - the shop manual instructs to do it in the water with a load, and using a tach (which on order) so I haven't yet. I'll try adjusting the idle mixture a bit to make it a bit more rich.

I wanted to try to determine if this sounds like something with the electrical / ignition system that may cause one cylinder to miss.

 

[b_arrington]

I checked the compression as suggested. Both cylinders tested equally at right about 100 psi. This is fine, I think? Shows equal performance anyway.

I fiddled with the idle mixture screw, about 1/8 turn at a time. No improvement, either richer or leaner. Richer made it worse. Still won't idle. I did notice that the plugs were pretty wet, more than usual. Not sure if this is from a problem or just that my fuel had a bit too much oil mixed in ( smokey exhaust)

I went through and reset all the link / sync settings by the book, but was too late at night to run up the engine. Will have to test another day, but any other suggestions?

 

[b_arrington]

I made some progress in the idling and it's much better now. Redoing the link / sync procedure helped, and I needed to increase the idle speed screw plus make the idle mixture a little richer.

I still have the unresolved clunk issue. I think the engine is intermittently missing. I made a video to show the symptoms.

Assuming it's missing, it occurs across the speed range. I have the engine set to idle at around 740-750 RPM. When the miss happens it will slow to 650-680 RPM and slowly recover to the set point. At the same time the engine will jerk and rotate clockwise. If the miss is big enough and the engine slows to under 620 RPM it will stall, as seen at the end of the video.

What would be causing this missing issue? I don't want to just throw parts at the problem. Thanks.

 

[racerone]

Use a timing light to see if you can find an ignition miss on this motor.

 

[b_arrington]

Use a timing light to see if you can find an ignition miss on this motor.

If there is a miss, what is the likely issue / resolution?

 

[racerone]

Well, you would have to do some inspection / testing as the motor is not on my work bench. ----Could be just a bad sparkplug.

 

[b_arrington]

Spark plugs are easy to replace, and cheap. However, I have replaced the spark plugs and the issue remains. So I think that rules out that source.

Could you suggest some items to test? I have a shop manual and have read through it and found no references for items to test or diagnostic procedures when the engine is missing. Absent some inkling of what to look at and a possible connection to the problem, the results of a test are not particularly meaningful.

An example of something that might be helpful is, the coil could be weak, check the output; or the powerpack is not likely to cause the issue; or if the magnets under the flywheel are old and weak it may cause this.

 

[racerone]

What kind of shop manual is it that does not guide you in trouble shooting.------Some aftermarket manuals are best used in the wee house with the 1/4 moon in the door !-----Answer this.----Does spark jump a gap of 7/16" or more on both leads , yes or no ?----Are you going to run with a timing light as a testing method , yes or no ?

 

[Newyota]

I have a 1998 Evinrude 15 hp. Model E15RECR, SN G04514576.

Problem
Currently the engine will not idle. It needs a good amount of throttle to stay running. Also at idle, I noticed an intermittent bur frequent "clunk" noise. At the same time as the "clunk" the engine torques to the starboard and the engine speed slows way down. If no throttle is applied, it will stall. It almost seems like one cylinder has misfired and is causing a stall. If the throttle is advanced there seems to be no "clunk". The clunk had been observed 2 seasons ago but went away.

Recent issue history
2 weeks ago the engine stopped running while in use and would not restart. Was diagnosed with a stuck float. After the float was freed the engine was not idling well at all (would die when tiller set to idle speed). High speed performance was fine and normal.

Recent work done
I had messed with the carb / settings for the no start issue, so I installed an OMC rebuilt kit. I used a shop manual to perform the sync / link adjustments post carb installation. I've done all up to the point of setting the idle speed / idle mixture adjustments in the water with a load. I'm waiting on a tachometer to do those.

After installing the carb kit and the doing initial adjustments the engine fired up right away and idled fine for about 5 minutes. I shut down and restarted; this is when it stopped idling and I observed the "clunk" and RPM decrease problem. It was while making adjustments on the stand with water muffs that the "clunk" and no-idle problem started.


The fuel pump is fairly new. The fuel pump screen is clean. Spark plugs were new this season and are the factory spec type. The fuel is fresh.

Thanks for any help with the no idle / clunking issue.

Seems like a lean sneeze.Did you check for any air/vacuum leaks?I recently sorted out some leaks that were causing me some issues.Mine would not idle well and would "clunk" and die at times.I do think I may of had a partial clog in my low speed/idle circuit.Any hose clamp/zip ties and gaskets such as intake should be checked..I assume you did a very good cleaning of the slow speed jets and circuits on the carb.Also, that has the plastic top carb also I believe.Make sure no cracks or leaks around the plastic top.

 

[b_arrington]

Seems like a lean sneeze.Did you check for any air/vacuum leaks?I recently sorted out some leaks that were causing me some issues.Mine would not idle well and would "clunk" and die at times.I do think I may of had a partial clog in my low speed/idle circuit.Any hose clamp/zip ties and gaskets such as intake should be checked..I assume you did a very good cleaning of the slow speed jets and circuits on the carb.Also, that has the plastic top carb also I believe.Make sure no cracks or leaks around the plastic top.

Thanks, I'll check these. I did do a very thorough cleaning of the carb. Fully disassembled, soaked, and cleaned. I'll look carefully at the top plate. I was careful to follow the tightening pattern when attaching it too.

 

[b_arrington]

I seem to have resolved my engine missing problem. TL;DR: corrosion on the power pack grounding ring caused the engine to miss.

I replaced the coil, which did not seem to help. Next I replaced the power pack. The power pack has a grounding ring that slips over the lower mounting bolt and grounds against the engine block. Upon removal I found the grounding ring had significant corrosion as did the grounding location on the aluminum block. I lightly sanded the block to remove the corrosion and make good contact.

The new power pack did not come with fiber washers. Several of the old ones could not be reused, and I didn't have new ones right away. I mounted it up but the lower bolt could not hold the power pack tightly against the block, meaning the grounding ring was loose. Upon sea trial the engine was missing VERY badly.

Installation of some new washers made the grounding ring contact the block. The missing situation was immediately resolved and the engine idles smoothly and reliably. My conclusion is that the corrosion on the grounding ring caused a poor electrical connection and the engine to miss. I attribute the idle resolution to the carb rebuild plus meticulously following the link/sync instructions.