Mystery cylinder problem, HELP needed! 1971 Evinrude Misfire on idle

[Sander]

Hello guys,

1971 Evinrude 100hp here, compression 120,120,115,115 - spark good. The cylinder number 3 seems to be misfiring and losing power, BUT, only on idle! Ignition ok, spark plugs good, I am in total confusion and loss on what is causing this problem , only thing I can think of is Carbon build up...perhaps some of you lads, more experienced than me could guide me in the right direction! It would mean a lot to me to get this motor running like it should. I just don't know what to do!

Thank you

 

[BonairII]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

Maybe a bad plug wire or bad spark plug? Swap the plug wire....see if the problem follows the wire. Then do the same with the plug.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

hey, Bonair - we have done that, that is how we figured that the cylinder # 3 had this problem.

 

[BonairII]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

Didn't see the "spark plugs good" in your post. I didn't see the where you changed plug wires though.

Couldn't hurt to decarb. It's a good thing to do regardless of whether you're having probs or not. I want to decarb my motor, but until I can get #2 and #4 cyls firing(or getting fuel)...I'm in a holding pattern.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

Just added seafoam to the fuel, ran it for about 40min, and seems like there is a little improvement. But still misfires quite often. Only on idle.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

Could a spark plug be bad internally, without any visible cracks/damage to the eye?

 

[dc095]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

If the plug fires in #2 and not #3, its not the plug.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

If the plug fires in #2 and not #3, its not the plug.

Hey DC, i have swapped the plugs and the problem still persists.

I have found a thread with a similar motor, and same problem. Unfortunately, the thread died out with out resolving the issue.

 

[Solittle]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

In addition to swapping plugs & wires to isolate to #3 did you also swap coils?

 

[BonairII]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

If not electrical...could this be a fuel issue?

 

[emdsapmgr]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

Are you sure you are losing spark at idle? It's easy to mistake a "lean sneeze" (carb problem) as an intermittent ignition issue.

 

[retiredfornow]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

What solittle said.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

In addition to swapping plugs & wires to isolate to #3 did you also swap coils?

I have not, how would I go about doing this Scolittle?

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

Are you sure you are losing spark at idle? It's easy to mistake a "lean sneeze" (carb problem) as an intermittent ignition issue.

I don't think we are losing spark. I am also not sure about the Carburetor, a friend told me it was fine, as it didn't hesitate to rev up. With Sea Foam added to my fuel tank now the cylinder is OK when removing plug wire, cylinder drop test (did not do drop RPM before, that is how we found the problem). You must forgive me for my lack of knowledge, and perhaps it might be a little hard to understand me.

There was a lot of carbon build up on all the plugs, he suggested this was the problem, however he was not sure. This is why I am trying to get help here, as Ive seen some very experienced members, and in a long shot someone that might have had a similar problem with an older outboard.

I do really appreciate your help that might lead me on the right track.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

If not electrical...could this be a fuel issue?

I should mention, we have replaced the fuel pump and all the hoses. As the old hoses had leaks, and the old pump was failing. However, it still could be a fuel issue your right, but it doesn't seem like it.

 

[Sander]

Re: Mystery problem, HELP needed! 1971 Evinrude

Re: Mystery problem, HELP needed! 1971 Evinrude

After a bit of better reading, this is the exact same problem that I have. It is really is disappointing that the person with the problem never reported back. Either he fixed it or gave up.

http://forums.iboats.com/showthread.php?t=500025&highlight=evinrude+misfire

 

[BigBassin78]

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Have you considered the thermostats, are one or more stuck open? This will cause major carbon build up very very quickly. Can you hold your hand on the motor when it is warmed up and running? This is likely not the answer but something to consider.

 

[BonairII]

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Is motor idled a lot? Or used at slow trolling speeds? That might explain why the plugs etc are all carboned up.

 

[Sander]

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Big : I can put my finger on the motor and hold it for a few seconds. I have not checked the thermostats, will look into this if my manual provides the information.

Bonair : The previous owner used the boat for pulling skiers/water sports. I am not looking for speed with this motor, I just want to cruise and occasionally fish. I have had the motor on water only once.
Going to buy new plugs tomorrow to have some for spare just in case, and will do a test with them but I am sure that is not the case.

I have found quite a bit of info searching the forums, but unfortunately none of the thread starters reported back, stating that they fixed it or not, and how. Especially the thread I linked.

 

[BonairII]

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

Re: Mystery cylinder problem, HELP needed! 1971 Evinrude

It's def frustrating following threads that just end for no apparent reason with no update on whether the prob got fixed or not.

Hang in there, you(we) will get this figured out. I can't get my own motor running right(yet), but it won't stop me from trying to help out others.....whether they want my "help" or not.