Spark gap jump on CD-11’s

[skanders01]

Can anyone help me with what is an acceptable spark gap jump for a ’54 Johnson 5.5? I have multiple motors I am working on and so far the gap jump capability seems to be anywhere from .040 to .070 among the four motors I am working on. I could not find any information in the big thick service manual I have.

PS. Has anyone ever had so much spare time that they put together and index section for the 10th edition of the Johnson Service Manual? 😆

Thanks in advance for any assistance.

Kyle Anderson
Trempeleau, WI
skanders@triwest.net
920-764-0501

[garry-in-michigan]

The Spark plug gap should be 0.030" – the breaker point gap should be 0.020" – and with those settings the spark should jump a 0.25" air gap (or 7 mm) minimum. That 5 horse is a low compression outboard. That was pretty much the standard until OMC went to electronic ignition for the higher compression motors with electric starting. You don’t want to crank one of those by hand. . . 🙂

[skanders01]

Thanks for the quick reply, Garry. I have an inline spark plug test light, so I will know I have spark, but wanted to "quantify" that spark, so I bought one of those cheap adjustable gap testers to see what that would do for me. They are graduated by voltage but I used a feeler gage instead. Having trouble getting them to start after rebuilding them, so I am troubleshooting the easy stuff first….the electrical!

Regards,

Kyle Anderson
Trempeleau, WI
skanders@triwest.net
920-764-0501

[frankr]

When I am working on a motor, I consider 1/4" open air spark gap as being good to go. Yeah, I know, some people look for 5/16 or even 3/8. It should be noted that the shape of the spark gap points makes a big difference. It is a lot easier for a spark to arc between two sharp pointed electrodes than two of another shape (round, flat, whatever). So that needs to be considered when evaluating spark by gap width.

[stanley]

The AOMCI store sells a nifty little spark tester that allows you to evaluate spark under compression.It’s not as cheap as others but gives a true evaluation of spark.

[jerry-ahrens]

I have always set my adjustable spark tester to a 1/4 inch air gap. The universal OMC magnetos should easily jump that if evrything is right. In fact, I usually grab my spark tester that looks like a spark plug with an alligator [ground] clip fastened to the side. Like this one….https://www.google.com/search?q=spark+t … IzkdB9M%3A

[Mumbles]

You can make these spark testers for cheap out of common items usually found in the shop. Open the gap to whatever you want and rope away!

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