1997 Johnson 70HP weak spark (DVA readings need some advice)

thefdmgroup

Cadet
Joined
Mar 23, 2013
Messages
8
Thank you in advance for any help!! Bought a boat with a 97 Johnson 70hp J70TLEUM. Upon first inspection it was a little dirty under the cowl but looked in order. Cranked right up on a cold start and idled and rev'd up on muffs no problem. Owner stated he thought it needed a carb job because it was acting sluggish lately and the boat sits unused alot. The next day I crank the boat up idles ok a little rough but then all of a sudden after a little while it gets really rough, pull the plug wires and discover weak spark on two cylinders and engine is only running off cylinder number 3. After fooling around, cylinder 2 gains a strong spark and then fails again. The following day I hook up a spark tester to find cylinders 1 and 2 have very weak spark and cylinder 3 strong an blue. Swap a few coils around and continue to only get a good spark on #3. After about an hour, I get weak spark on all cylinders and now the engine will not fire. Pulled out the multi-meter and DVA and here is where I am now. I am new to outboard engines but work on vintage bike and cars so I can follow directions well.

The test results are as follows:

Compression 120-115-120

Stator
Brown to Brown Yellow- resistance 745 / DVA 296v
Orange to Orange Black- resistance 400 / DVA 172v

Timer
White to Purple- resistance 110k / DVA 2.1v
White to Blue- resistance 112k / DVA 2.1v
White to Green- resistance 112k / DVA 2.1v

Power Pack
Orange Blue to Blue- resistance 138
Orange to Green- resistance 0
Orange Green to Purple- resistance 0

When testing from ground to each of the orange wires on the coil DVA registered 148v

Now it seems one of many components are failing, some of the tests. With so many odd readings I'm hoping someone can make sense of what is happening to this ignition system or is everything just broken.

Looking forward to some good input, THANKS AGAIN!
 

thefdmgroup

Cadet
Joined
Mar 23, 2013
Messages
8
Re: 1997 Johnson 70HP weak spark (DVA readings need some advice)

Bump bump, any ideas anyone?
 

JDusza

Ensign
Joined
Apr 21, 2009
Messages
934
Re: 1997 Johnson 70HP weak spark (DVA readings need some advice)

Not everyone! ha ha ha
CDI has an excellent troubleshooting guide. You have the tools and know-how to solve this.
cdielectronics.com/technical support/troubleshooting guide
They'll help you with the specific numbers. I can, but, you can do it just as easily.
Very unlikely the stator or timer base is whacked (because it does run), more likely you're experiencing high voltage leakage from old parts. Run the engine in the dark and look for sparks to ground. My guess is that you'll see plenty.
You'll become the expert with cdi and the dva.
J
p.s., no. you are not totally broken.
 

thefdmgroup

Cadet
Joined
Mar 23, 2013
Messages
8
Re: 1997 Johnson 70HP weak spark (DVA readings need some advice)

Thanks, JDusza,
Today's progress, checked the gap on the plugs just to be sure and seemed the gap was a little off, and then notice the terminals on the plugs were loose. Tightend them up and went on to double check every ground, took sandpaper to the coil grounds and the mounting surface and cleaned them up, double checked my spark tester and i'm getting spark now on all three cylinders.

Engine cranked up and runs a little rough but appears to be running on all three now, but we def. have carb issues as fuel is spitting out the front of them, and I think the carbs may be flooding the engine and fouling the plugs. Going to rebuild carbs and see what we have. I really hope it was just a bad ground and we dont continue to have spark issues.

I will update when we have progress!

Thanks again!
 

clanton

Rear Admiral
Joined
Jul 9, 2001
Messages
4,876
Re: 1997 Johnson 70HP weak spark (DVA readings need some advice)

If you are getting voltage readings from the brown, and the orange wires to ground, the coil under the flywheel is shorted to ground.
Dav readings for the 2 orange wires seems to be way too high. These power the logic in the pack.

Check the wires behind the plate the pack mounts on, and plate mounting bolts. You look for loose bolts and frayed wires.
Check all pack ground wires
 
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