'78 Evinrude 15hp - help needed

[thunderfog]

As the topic shows, I have a '78 Evinrude 15hp. Background since I've owned it for 3 years -- I was chasing an electrical issue, so I just had all of the components replaced. LAst summer, it didn't get much use... just a few hours, but it ran fine. 4 hours of use this year, and the upper cylinder cut out on me. I pulled the cover and disconnected the wire, and upon reconnecting the wire to the plug, discovered that if the wire sits halfway on the plug, the electrical connection is completed, and the cylinder comes back to life. Insert it all the way back on the plug, and it cuts out.

Again, the coils, wires, and plugs are all relatively new.

Any ideas?

Important edit: this issue is why I had the electrical components replaced to begin with.

 

[Kamele0N]

 

[46Harry]

There is a real good possibility that the spark plug is fouled. When you pull the plug lead away from the plug the gap intensifies the spark causing the plug to fire. Sometimes you can run the engine like that for a few minutes and the plug will clean itself.

 

[thunderfog]

Originally Posted By: 46Harry
There is a real good possibility that the spark plug is fouled. When you pull the plug lead away from the plug the gap intensifies the spark causing the plug to fire. Sometimes you can run the engine like that for a few minutes and the plug will clean itself.


Plugs for both cylinders look the same and I swapped them with the same result. I'll probably replace the wire again, but it confounds me as to why this engine seems to be eating spark plug wires on the upper cylinder.

 

[Fastcompany]

Check your spark voltage and resistance values for your plug wires and coils. Spark voltage can be checked by a little tool at the auto parts store that let's you open up the gap and actually see the spark. Should have a nice strong spark with the gap opened fairly far. Also be sure you are running copper plugs. Platinum does not conduct as well and requires more power to spark. Make sure you plug gap is set correctly. Sounds to me like something is grounding out. Never heard of pulling a wire making spark stronger. Any time you have an air gap you are introducing resistance. Air has alot of it. For the coils I don't know the spec on what you have but check the primary and secondary resistance of both coils so you can check one against the other.

 

[Fastcompany]

Oh also. Are you running resistor plug ends? If so there are many on the market that are absolutely junk. Make sure you get the specified resistance with the end pulled off the wire. And if you are running those you should also have solid core wires and a non resistor plug. I'm not familiar with your engine but what does it use for a pickup? If the timing is off adding resistance produces a longer weaker spark and taking it away gives shorter stronger spark. Hope some of that helps you.

 

[L_Sludger]

Originally Posted By: Kamele0N

Can you explain this picture please?

 

[bmod305]

This website covers 9.9/15hp:

http://www.leeroysramblings.com/Johnson 9.9_15.htm

 

[BrocLuno]

If the plug fires with the wire slightly off, the wire is prolly OK. As you do that, you develop dual gaps. That increases discharge resistance and forces the coil to charge to a slightly higher rate before it'll jump the gaps.

It may be a weak coil. I'd swap the coils and see if the problem follows the coil...

Also, try fine-wire platinum resistor plugs and see what happens ...

The spark gap voltage tester is a good way to test outboard ignitions. Lisle 20700 is a pretty good one

 

[Linctex]

Spark plug wire "ends" (the boot picture) often go bad.

It's worth it to try a new one.

 

[BrocLuno]

Except as far as I know, in 1978 all OMC outboards used plain rubber 90* boots with a spiral spring and no built-in resistor ...

The one shown above is common on motorcycles and some OPE ...