75 HP Evinrude "breaking up" at WOT

[npd4432]

When operating usually at WOT between 5500 and 5800 RPM the motor seems to cut out for short periods (for about a second) and then continues as normal. This seems to me to be an electrical ignition or spark problem. My question is where do I start to try to diagnose the problem? Plugs, wires, coil packs, ignition module?????? Could it be something else?

 

[Lodgepole]

Re: 75 HP Evinrude "breaking up" at WOT

It is not banging like you hit a log or something? (shift dog worn) Otherwise you might be sucking air into the fuel line or have the beginnings of fuel pump failure.

 

[HighTrim]

Re: 75 HP Evinrude "breaking up" at WOT

Have you done a spark test to see if you are dropping a cylinder?

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

I have done a spark test at idle, all good. Dont know at WOT. It seems as if somebody is very quickly hitting a kill switch for fractions of a second at intervals of about 10-30 seconds. Not a "log bang". I did recently though have a fuel tank issue with the quick disconect. I will replace both the male and female end and see if this recitifes the problem.

 

[freetime99]

Re: 75 HP Evinrude "breaking up" at WOT

It sounds like one of the ignition coils is not grounded properly, may have some corrosion on one of the mounting bolt(s). A freind of mine had the exact same problem you're desribing, and found that to be the case. He unbolted all three, cleaned the bolts and mounting surfaces , reinstalled them- the problem went away.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

I will also try to clean up the coil packs too.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

Problem still persists, I have changed the fuel line, primer ball, fuel tank brass fitting, cleaned coil packs as described, but still have the problem. It doesn't happen all the time, but usually at WOT near around 5600-5800 rpm.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

???

 

[iwombat]

Re: 75 HP Evinrude "breaking up" at WOT

An electrical problem tied to a specific RPM range is a pretty rare animal. I'd expect to see some kind of problem at lower RPMs. Only thing I can think of is the rev limiter in the powerpacks is triggering early.

What year is this motor by the way, is this the '83 in your sig line?

I'd be looking at cleaning the carbs, especially the main jets. I think that's a more likely candidate.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

Yep it is the 83. I am going to try to rebuild the fuel pump, I just ordered the kit. After that I will clean the carbs. Is there a rev limiter in my motor??

 

[iwombat]

Re: 75 HP Evinrude "breaking up" at WOT

I _think_ just about all the power packs have rev limiters. (Disclaimer: This thought is based on very little experience and actual data in the matter) The ones I know about are designed to limit in the upper reaches of 6k. Its a stretch, but maybe this one is chiming in early.

Like I said though, I'd suspect dirty mains, or even a mis-adjusted advance timing over anything electrical given such a narrow range of mis-behavior. Given the symptoms as described, I think fuel pump would kind of be a long-shot too.

 

[Chinewalker]

Re: 75 HP Evinrude "breaking up" at WOT

I am pretty sure that it is not fuel related, as that is rarely an instantaneous off/on thing. All three carbs do not run out of fuel at the exact same moment. I doubt it is a coil issue, too, as all three would not cut out at the same time. Could be a powerpack - make sure the ground wire for the pack is clean and grounding properly. Could be the trigger - make sure none of the wires that exit it are touching anything as the trigger advances/retards. Could also be the kill wire circuit, as that would affect all three cylinders at the same time.
- Scott

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

What is the "trigger"? And which of the wires are the kill circuit? Like I stated before it seems as if someone is hitting a kill switch for a fraction of a second, wait about 10-30 more seconds, it breaks up again. Sometimes after a while it just goes away. I will clean the ground for the power pack. Could it just be one of the coils acting up and not all three together? By the way all of the coils and the powerpack are orig. equipment (24 years old) I may just replace all of them for piece of mind.

 

[iwombat]

Re: 75 HP Evinrude "breaking up" at WOT

I like Chinewalker's answer. Better yet, after reading that I think I understand the symptom better now too. I had something else stuck in my head. Now that I go back and read . . . well you know.

Now, I don't think a lean-lag fits the problem as described very well. So, I'm off the whole dirty main jet bandwagon.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

I did just rebuild and clean the carbs at the begining of the season, they didn't even need it they were very clean.

 

[jtexas]

Re: 75 HP Evinrude "breaking up" at WOT

a float that sticks intermittently will give you just that symptom - one cyl starved of fuel every once in awhile.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

Update, I have rebuilt the fuel pump as suggested and still have the same problem. I have noticed the problem has happened at trolling speed but is not as prevelent and for longer periods. Any suggestions??

 

[CharlieB]

Re: 75 HP Evinrude "breaking up" at WOT

Adjust the shift cable about TWO turns to put just a touch MORE pressure holding into forward gear.


Couple of us chased our tails for days one a 90, swore it was failing igniton, turned out it was trying to jump out of gear at full load/throttle, part throttle would STILL do it only took more time between 'jumps' with we all thought to be that the ignition took longer to heat/fail.

Bias the shifter towards forward and re-test.

 

[npd4432]

Re: 75 HP Evinrude "breaking up" at WOT

Adjust the shift cable about TWO turns to put just a touch MORE pressure holding into forward gear.


Couple of us chased our tails for days one a 90, swore it was failing igniton, turned out it was trying to jump out of gear at full load/throttle, part throttle would STILL do it only took more time between 'jumps' with we all thought to be that the ignition took longer to heat/fail.

Bias the shifter towards forward and re-test.

Do you mean the shift cable, or the rod? If the cable what way (clockwise or counter clockwise) is the bias toward forward?

 

[CharlieB]

Re: 75 HP Evinrude "breaking up" at WOT

Truthfully, I'd have to look to be sure.

Look at your cable in neutral, then again in forward

If the cable pulled then turn clockwise

If the cable pushed then turn counterclockwise

Retest on the water and let us know, did it improve, longer in between 'jumps'

if so then add another two turns and retest.

If this is a new condition on a boat you've had for a while AND if this cures your problem then I would suggest you soon replace that control cable, it is stretched and not pulling the shifter all the way into gear.

If you recently had the foot off you may have turned the shift rod and changed that adjustment.