115 Johnson outboard with low spark

makorazor

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Apr 5, 2007
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Well I have spent two days searching over the 50,000 posts and have found my self lost in a sea of anguish. Ive got an early 70ish 115 johnson outboard that seems to be in very good condition but will not start due to low spark. It has enough to give you a good zap and seems to firing in a regulator pattern but not enough to visibly see spark to the motor. This motor has the old style ignition with a single coil pack, small round rectifier, and what i believe is the non water cooled voltage regulator next to it. I found the info on testing the rectifier that I will test today but I believe that its having charging issues. I also read that the ignition system is powered directly from the charging system and not from battery power. I did notice that there is a random (obviously added by some one) a power wire running haphazardly from the positive post of the starter motor to the power terminal supplying power to the ignition box. Under cranking conditions I measured 7v on that terminal and I believe that my be where the power for the ignition system is coming from rather than the charging system. anyone have a diagram or know what the voltages I should have coming out of the regulator / to the ignition / etc. should be? I would guess 12vdc but Im not an outboard tech. Thank you all for the wealth of information!

(ill take some pics today, that may help)

Jason Woods
Northern CA
 

ezeke

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Sep 19, 2003
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12,532
Re: 115 Johnson outboard with low spark

On the 73-77 115HP fire is what you must have, BUT, you need to be turning at 300RPM to get enough and that requires a big, fully charged battery.

If you have fresh fuel and a fully closed choke, jump your starting battery to another battery to increase the power and see if the motor doesn't start.

You can take the rectifier off the motor if you want, it has nothing whatever to do wiith starting your engine; the only purpose is to charge the battery.

The rectifier simply converts the alternating current from the magneto to direct current by the use of diodes, which allow current to pass in only one direction. You test the rectifier by disconnecting it and, using the case as ground, check each wire in both directions with your ohmmeter. If you get a similar reading on a wire in both directions, a diode is probably burned and the rectifier needs to be replaced.
 

makorazor

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Re: 115 Johnson outboard with low spark

I have been testing it with the plugs out so I know its spinning way faster than it would under normal starting conditions so thats pretty much out. The reason I believe it to be the charging system is the posts I have read that the ignition system is not powered via the battery only by the induction system. Thus I inferred that if the rectifier is not putting out DC voltage or at leased enough I would have a weak spark. I would guess then that the voltage coming off the rectifier would be = the speed at witch the motor is spinning and that the voltage regulator (box next to it) would take what ever voltage the rectifier is putting out and regulate it to 12v? The highest voltage I have measure going into my ignition box was 7v and that with my weird wire coming off the starter post. Ill check again but I don't think there is any voltage coming off the regulator.

Thanks again for your help~

Jason Woods
d:)
 

ezeke

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Re: 115 Johnson outboard with low spark

Even better than a picture would be a model number off the transom bracket or the welch plug on the engine block.
 

makorazor

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Re: 115 Johnson outboard with low spark


It is a 1970 according to my sources model number

#115ESC70D

I also tested the rectifier and found the following,

Each of the three wires (red, yellow, yellow) tested to the case (ground) = nothing in both directions. My tester can check up to 2 mega ohms and still nothing.

I then tested Red to yellow in both directions, one direction no reading the other was over 2 mega ohms beyond the ability of my tester.

I was expecting to measure resistance in both directions for a faulty unit not neither...

Heres a pic of what Im up against, Still trying to figure out the random wire from the starter to the ignition?? Weird

Thanks again!

Jason
 

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makorazor

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Re: 115 Johnson outboard with low spark

Guess that was to big.... lets try again[
 

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makorazor

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115 Johnson outboard with low spark

I'm nearing panic now as I have a new ROV (remotely opperated vehicle) prototype we need to get in the water and we are stranded until we get this motor sorted.


I have also been reading now several experts saying that the rectifier has nothing to do with the ignition at all. After reviewing pics of other later model engines Im starting to see why. Most of the 72+ motors have a second set of coils that produce DC voltage to power the ignition (from what I gather) My 1970 however has only 2 wires and one set of coils producing AC voltage. So somethings got to give. Is my ignition being powered by my battery or by my alternator and thus my rectifier? Im going to try a spark tester today to see where I stand with the non visible (but present) spark, any assistance with this would be greatly appreciated!

Jason Woods
 

makorazor

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Apr 5, 2007
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Re: 115 Johnson outboard with low spark

I did and thank you for that, but I couldn't find anything on a 1970 115hp

Im not sure what ignition type I have so I wasent able to reference another motor.

Jason
 

bowrider

Petty Officer 2nd Class
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Feb 23, 2007
Messages
107
Re: 115 Johnson outboard with low spark

I t wouldn't hurt check resistance on the plug wires, just in case...
 

makorazor

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Apr 5, 2007
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Re: 115 Johnson outboard with low spark

I tried checking voltage directly off the coil pack so its some where before there. I tested again today and as luck would have it I now have no spark at all. Time to part it out on ebay....

Jason
 
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