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jamesan
'79 55hp evinrude has an occassional misfire. By occassional I mean that when the throttle is advanced enough to give the small boat some speed the motor starts running very smoothly EXCEPT about every 5-20 seconds it misfires 1 time. The engine sort of goes "BAM", and then it runs perfect for another 5-20 seconds before misfiring again. It goes on constantly regardless if the engine is cold or warm. It certainly seems like a spark problem (replaced the plugs already) that only shows up under higher rpm's.

From the manual I have learned that it is a Type II Capacitor Discharge Ignition.  I do not know exactly how to troubleshoot this problem as it is difficult to simulate the high rpm's at home.

Any thoughts?
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taglic

Make sure your spark advance is working correctly. If it stays retarded and the throttle is increased it will go "BAM" as you put it. What happens is the revs are too high, the ignition is too late and the exhaust ends up blowing back into the crankcase. Check the timing at idle and WOT, (Wide open throttle) under load.

Carl Tagliabue
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jamesan
Thanks,
 I haven't had a chance yet to check the timing. But I do know that it moves with the throttle. I have noticed that it does move sluggishly. Is that normal? Seems to me like the pivot point needs to be cleaned.

 I tried to ask an outboard tech about it, but he would not answer, he would only say "DON'T MESS WITH ANYTHING, YOU WILL JUST GET IT ALL OUT OF ALIGNMENT!" He was one of those that thinks only an outboard mechanic can work on an outboard. I am not experienced with outboards, but that shouldn't stop me from working on it.

Thanks again for your help...
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taglic
It should move freely and advance from about 20 to 35 degrees, fully retarded to full advance depending on the motor design.

Carl Tagliabue
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