Johnson 120hp, Odd Acting Cylinder

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Pokertrampp

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I have a 1988 120hp Johnson, that starts and runs, all cylinders have 100+ psi and all have spark that will jump a 7/16" but the motor runs rough and when I pull the plug wires it runs worse, except when I pull the top Right plug it does not change the way it runs. what could this be, I thought maybe the cdi box but that is too expensive a part to just go buy and hope. I have double checked the compression and spark to make sure.

Things I have done so far:
1) Rebuilt Carbs.
2) Changed Spark Plugs (Champion QL77JC4 gapped at .040)
3) Changed Coil on bad Cylinder (Made no difference) the coil was a new one not one from another cylinder, I am going to swap one with a working cylinder to see if the problem moves.

I am thinking maybe a bad cdi but not sure since it has spark, or a timing issue, but not sure what to check next to eliminate the timing issue my manual does not mention any timing adjustments. I see a spark advance knob but it does not change the way it runs. also the miss is ther even when I increase rpms sometimes the mis gets worse and the motor acts like its going to stall and the revs back up and other times it just stalls.
 
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rodbolt

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Re: Odd Acting Cylinder

Re: Odd Acting Cylinder

I would double check that carb.
 
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mikesea

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Re: Odd Acting Cylinder

Re: Odd Acting Cylinder

DO you have problems at wide open throttle as well?try spraying some mixed fuel into the suspect carb throat,if the cyl fires ,you still have carb issues
 
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Pokertrampp

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Re: Odd Acting Cylinder

Re: Odd Acting Cylinder

i noticed today that the plugs are wet when i remove them right after i run the motor. does this mean anything, it is all 4 cylionders not just the odd acting one.
 
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ezeke

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Re: Johnson 120hp, Odd Acting Cylinder

Don't pull plug wires on that particular engine while it is running, you will damage the powerpack and have to replace it.

Get an inductive timing light so you can "read" the firing across a range of RPM.
 
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F_R

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Re: Johnson 120hp, Odd Acting Cylinder

You have 7/16 spark, so it isn't the power pack. In fact, I wonder if you actually have any problem at all. It is often hard to tell a difference when you kill one cylinder at idle.

If there is a problem, it may be a rich/lean difference.

Make sure there is no water getting into that cylinder.

Don't be freaking out over oil on the plugs---that's normal.
 
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daselbee

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Re: Johnson 120hp, Odd Acting Cylinder

ezeke said:
Don't pull plug wires on that particular engine while it is running, you will damage the powerpack and have to replace it.

Get an inductive timing light so you can "read" the firing across a range of RPM.
Click to expand...

I just had the same thing on a 1990 120 looper. Spraying carb cleaner in each carb caused the expected bogging at idle, except for cylinder #2.
So, I did a spark gap test, and all cyls jumped 7/16".
SO, I did exactly as ezeke suggests...put a timing light on each one, look into the light when idling, and it was immediately apparent that #2 was firing erratically. The others were firing very evenly. It was very obvious.
I have a Stevens ignition breakout box, and with my DVA meter I debugged it down to a bad timer base.
New timer base, all cyls firing right, and engine running as it should.
 
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Pokertrampp

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Re: Johnson 120hp, Odd Acting Cylinder

daselbee said:
I just had the same thing on a 1990 120 looper. Spraying carb cleaner in each carb caused the expected bogging at idle, except for cylinder #2.
So, I did a spark gap test, and all cyls jumped 7/16".
SO, I did exactly as ezeke suggests...put a timing light on each one, look into the light when idling, and it was immediately apparent that #2 was firing erratically. The others were firing very evenly. It was very obvious.
I have a Stevens ignition breakout box, and with my DVA meter I debugged it down to a bad timer base.
New timer base, all cyls firing right, and engine running as it should.
Click to expand...

Is there a way to test it without the above mentioned equipment? I have a regular digital volt meter, and a regular timing light.
 
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G DANE

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Re: Johnson 120hp, Odd Acting Cylinder

I would check the reed leaves too.
 
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daselbee

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Re: Johnson 120hp, Odd Acting Cylinder

You need a DVA adapter for your digital voltmeter. When debugging the ignition system, you are reading what is called "peak AC voltages". The DVA adapter sort of captures those peak pulses, and allows you to read the values on a regular meter set for DC voltage measurement.
For instance, the primary wire of the coil (small orange one) should read over 150 vDC at cranking speed using the DVA adapter. You can get them on eBay.

Use the timing light and look into it as I described. You may or may not see the obvious erratic spark pattern. You want it to look consistent and regular when flashing.

The Stevens breakout box is a luxury item.....allows you to easily measure the system's voltages without piercing the insulation.
 
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Pokertrampp

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Re: Johnson 120hp, Odd Acting Cylinder

The fact that the plug is wet on the odd cylinder seems to indicate the carbs are not the problem, is that correct?

I am going to pick up the test equipment this weekend as well as a new Seloc Manual since the current one I have does not seem to be very helpful.
 
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ezeke

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Pokertrampp

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Re: Johnson 120hp, Odd Acting Cylinder

ezeke said:
None of the Seloc manuals are specific enough to deal with ignition/electrical problems on your engine. You need the factory manual for your specific motor - part #0507664.

Example: http://cgi.ebay.com/ebaymotors/1988...Motors_Manuals_Literature&hash=item2eab5f92b4

To go very far with your ignition testing requires a DVA for your multimeter: http://www.usatoolwarehouse.com/usatoolwarehouse/ESI-640.html
Click to expand...

Is it possible to get that manual digitally? I already ordered the Seloc Manual, so I hope its not as useless as the manual I currently have.
 
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Pokertrampp

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Re: Johnson 120hp, Odd Acting Cylinder

My manual states:

1. Check the timer bases resistance from the white wire to the blue, green, pink and purple wires. Reading should be 38-42 ohms.
2. Check the DVA output from the timer base. A reading of at least 0.5V or more from the white wire to the blue, green, pink and purple wires (while connected to the pack) is needed to fire the pack.
3. Check the DVA output on the orange wires from the power pack while connected to the ignition coils. You should have a reading of at least 150V or more. If the reading is low on one cylinder, disconnect the orange wire from the ignition coil for that cylinder and reconnect it to a load resistor. Retest. If the reading is now good, the ignition coil is likely bad. A continued low reading indicates a bad power pack.

It does not say if the I take these readings while the motor is at rest or while turning it over. I will be checking it this weekend and I am trying to study up on the procedure so I can understand what I need to do, if there is anything else I should check please let me know.
 
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