93 Johnson 70 Compression Question

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PRussell85

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Jul 22, 2011
Messages
7
Hello,

My motor is a 93 Johnson 70 that is running pretty rough(sputtering, slight backfire, not idling well). I put an inline spark tester on the plugs and the #2 cylinder has very irregular spark. The others 2 cylinders are regular and strong (7/16" gap in spark tester).

When I checked compression I got 120-100-120 so at this point I have the thought that maybe this is the best this motor can run in its current condition.

I do not want to spend money on ignition componets to fix the irregularity on the #2 if the motor wont run well with these compression numbers.

Hopefully someone can give me an idea of what a compression difference like this will cause. If the motor will run well like this then the next step is fixing the ignition and hopefully all will be well.

Any thoughts are very much appreciated...

Russell
 
jbjennings

jbjennings

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Jul 18, 2007
Messages
3,903
Re: 93 Johnson 70 Compression Question

I believe it will run pretty good with that compression, although I also think it's very borderline. I would also clean the carburetors, and see if the carburetor on the low compression cylinder is dirty (sometimes you can't even tell when cleaning it). There's got to be a reason you have a cylinder that is that different. It could be a bad head gasket, also. Check your plugs for steam cleaning, rust, or milky stuff.
If it were mine, I'd go ahead and see if I had a bad coil and get good spark on all cylinders. I think it's worth it.
JMO,
JBJ
 
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PRussell85

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Jul 22, 2011
Messages
7
Re: 93 Johnson 70 Compression Question

Well Ill go ahead and try and fix the irregular spark then. FYI- I put a known good coil on that cylinder and still had the same issues. After running the spark plug is wet and oily as are all the rest. What should I be looking for now?
 
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PRussell85

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Jul 22, 2011
Messages
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Re: 93 Johnson 70 Compression Question

Any thoughts? Just need a little help to get the troubleshooting going...
 
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PRussell85

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Jul 22, 2011
Messages
7
Re: 93 Johnson 70 Compression Question

Does anyone know the WOT timing for this motor? The rubber stopper is gone so I fear its not adjusted correctly.
 
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PRussell85

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Jul 22, 2011
Messages
7
Re: 93 Johnson 70 Compression Question

OK, After a few days of working on this guy here's the story. Decarbed, brought the compression up on the number 2... it's now 110 so that's great. Cleaned carbs and when I finally got the idle mixture needles set the motor idled like a dream. Spark tester showed a consistent spark on all cylinders and again It idled perfectly smooth.

Today I was gonna take it to the river and when i fired it up on the muffs, it ran like it did to begin with (very badly). Put the spark tester on again and 1 and 3 were sparking fine...it was the number 2 acting up again. So here goes the troubleshooting-

New spark plug---no help
New plug wire---no help
New coil---no help

A few more clues-

-Sparks about every one second when first cranked and then no spark after about 7 seconds (could it be related to quickstart?)
-A few times started sparking fine for no apparent reason


I just don't know where to go next. Im not sure how to test a powerpack or timer base. Please help!!!
 
Last edited:
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Daviet

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Sep 24, 2008
Messages
8,958
Re: 93 Johnson 70 Compression Question

It might be time to invest in a factory manual, it will have specs and troubleshooting sections in it.
 
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