weak or erratic spark

[strangerdanger]

1977 Evinrude 115. Has anyone ever had a problem with the engine firing up and running but running rough due to the coils firing then they quit then just when you think its going to die they start firing again really strong for a few seconds then going back to being very inconsistent. Ive replaced a lot parts on this engine including all four coils. because of this issue the engine refuses to idle correctly. I could use some help.

 

[racerone]

What are the compression readings on this engine.-----What parts have you replaced.----What testing if any led you to replace parts ?

 

[strangerdanger]

The compression reading are 95# across the board. Ive replaced the coils. fuel pump, waterpump, intake manifold, carbs with rebuilt ones, all the fuel lines, and ground wires. It will actually run ok at full throttle but everything short of that is very inconsistent. Oh and the rectifier due to the battery not charging and the wires coming off of it where dry rotted and cracked

 

[strangerdanger]

I changed the coils because of the engine missing, Intake because of a crack, carbs due to the old ones being worn out. Fuel pump due to the surging of the idle going up and down which I believe this firing issue is the cause of whole problem.

 

[racerone]

95 is way too low.

 

[strangerdanger]

Ive had engines with less than that run and fire smoothly. Do you have any idea of what can cause the firing issues?

 

[racerone]

Use a timing light to find the misfiring cylinder.----Does spark jump a gap of 7/16" or more on all leads , yes or no ?

 

[strangerdanger]

I know the compression isn't the best out there but it is good enough run and idle. which it does until this firing issue comes around.

 

[strangerdanger]

Yes the spark will jump the gap. While I was doing the test I noticed that the spark would stop for a sec then come back. It was like it was pausing. It did it on all four cylinders. The number one was the worst one

 

[racerone]

Take ohm readings on stator and sensor coils.

 

[strangerdanger]

yes the readings on the stator are 1.4 on the yellow wires and .685 on the two brown wires going to the power pack.

 

[strangerdanger]

Oh and nothing going to ground

 

[strangerdanger]

I don't have a DVA but I did put my volt meter on the two brown wires and tested them to ground with engine running and one put out 21 volts ac and the other 36volts as

 

[strangerdanger]

did ya leave me?

 

[flyingscott]

How did your carbs wear out? You do not mention anything about the powerpak were they tested? Did.you put the correct carbs on the motor? That compression is bad get a different gauge and re-test.

 

[strangerdanger]

yes I put the same ones back on. there was slack in the butterflies. no I haven't tested the powerpack. not sure how without a DVA. All my manual talks about is using a DVA. you could be right about my guage. its not a expensive one. after going back out to the boat the problem seems to be with the #1 and #3 cylinders. #2 and #4 seemed to fire just fine. didn't want to switch any wires around cause I didn't want to short anything out.