1998 evinrude 25 hp intermittent miss

I have a 25 hp evinrude shows good spark most of the time at idle. The higher the rpms, the weaker the spark gets on the top cylinder only. Replaced both coils no difference. Not sure if it is power pack or stator issues. Any advice appreciated.

How did you determine the weaker spark at higher RPM.----What other trouble shooting has been done.-----Has water pump impeller been replaced ?

racerone said:

How did you determine the weaker spark at higher RPM.----What other trouble shooting has been done.-----Has water pump impeller been replaced ?

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i used an inline spark tester that has a viewing glass on both cylinders. Bottom stays bright and solid while top decreases in intensity as rpms increase,.

i also rebuilt carb, fuel pump and replaced impeller.

Thanks for the reply

This is a strange action, like an internal arcing inside the coil, which can get worse as rpm's increase. Since you replaced the coils we can rule that out. Gotta be in the powerpack, but this is an uncommon symptom.

timguy said:

This is a strange action, like an internal arcing inside the coil, which can get worse as rpm's increase. Since you replaced the coils we can rule that out. Gotta be in the powerpack, but this is an uncommon symptom.

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Thanks for your input. Does anyone know how the power pack is constructed? If it is one unit providing energy to both coils/cylinders it cant be the issue. If it has 2 separate internal “capacitors” or whatever component is used it could be the issue.

also, since i am getting spark all the way to plugs at idle, can I begin by ruling out stator issues?

I greatly appreciate the help. I am new to boat motors but am “Dangerously Mechanically Inclined”. Lol

thanks again

Put bottom coil on the top cylinder, top coil on bottom and test run again.

Thank you. I have done that as well as replacing coils and trading spark plug wires. I also replaced spark plugs.

Sorry ----I guess I missed that fact in your posting.----Should not be hard to figure out what is wrong.

The stator supplies energy to the powerpack which is allowed to release it's capacitor stored energy at the correct time by the "trigger", which creates it's own energy also by electromagnetic generation. A brilliant innovation to get rid of having to rotate the entire stator plate in order to adjust timing. This power is then converted to high voltage at the final coils. Yes, the powerpack can develop a weak or dead side. You can check that with a DVA meter which records the "peak" voltage. The concept was engineered to provide stronger and more reliable ignition while eliminating moving parts that can fail and wear out....like breaker points. I, personally question whether or not that objective was ever effectively met.