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  1. #1

    Default 72 Johnson 100 HP Ignition Problem 100ESL72R

    My '72 Johnson 100 HP barely runs with number 1 plug wire on plug. When I disconnect it, it starts easy and is strong on 3 cylinders. Plug was loaded up and replaced with no resolution. Am checking for possible cracks in distributor cap and possible shorts. Wires from pickup/trigger were pinched under cap with insulation damaged fixed insulation. Problem continues. The ignition system was upgraded with a CDI Pulse Pack/Amplifier, single coil, and pick up. Could the wire problem under cap and possible ground out have caused a problem with pulse pack? Need help to diagnose!.

  2. #2
    Join Date
    Feb 2001
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    Central West Florida
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    That type problem is normally caused by the related wire at the distributor cap arcing to ground... OR... a slight crack in the distributor cap allowing the spark to arc through to ground.

    Difficult to locate at times.... visualize closely in a darkened area, plugs out with spark nowhere to go excepting to the easiest escape route so to speak.
    We occasionally have questions. If you fail to answer, it may affect ours.

  3. #3

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Thank you Joe. I will try to run it on muffs at nite with number 1 plug wire on plug to see if spark jumps to ground somewhere. It runs much better with that plug wire disconnected. The shop manual mentions filling each wire tower 1/3 full with OMC type D grease. Is that simply dielectric grease?

  4. #4
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    That would be my guess.
    We occasionally have questions. If you fail to answer, it may affect ours.

  5. #5
    Join Date
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Was the distributor cap replaced , yes , no , do not know ?

  6. #6
    Join Date
    Jun 2013
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    Duluth Mn
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Mark proper #1 firing on flywheel and check with timing light. You may find a double fire. That's why it actually messes up the running. The repair you did may have to be reviewed.

  7. #7

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    I don't know if the cap was ever replaced. I bought the motor used. The parts are really expensive if you can get them. I saw a new old stock one for $295 and the CDI trigger dor $198. I need to be sure on the part I need.

  8. #8

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    I do't think the plug was firing but I'll check it out. The plug was oil fouled so I put a new plug in. It really runs bad when the number 1 plug wire is connected. It starts easy and runs pretty good on 3 cylinders.

  9. #9
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    Jun 2013
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    357

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    The plug is firing before it should perhaps causing the power loss as you describe. Have you done a compression check to see if the motor is sound and then worthy of repair?

  10. #10
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    ontario
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    I am not there to do the simple checks.----I would be checking where the rotor is pointing for each cylinder.---Also check the numbers on the wires compared to numbers on the distributor cap.

  11. #11

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Thank you for your help. Does the stator have any play in this type of ignition problem?

  12. #12
    Join Date
    Feb 2001
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    Central West Florida
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    The stator on that model pertains only to the battery charging system. It has nothing to do with the ignition system.

    As "racerone" suggests, check the cylinder firing numbers on the distributor cap. Having a spark plug wire connected to a spark plug SHOULD NOT cause a loss of power UNLESS the plug wire is connected to the wrong firing position at the distributor cap.

    Just in case..... The engine cylinder numbers, standing in back of the engine, facing the spark plugs, are numbered as follows:

    2.....1
    4.....3
    Last edited by joereeves; 09-05-2017 at 09:47 AM.
    We occasionally have questions. If you fail to answer, it may affect ours.

  13. #13

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Thanks for your help. Now that the storms have cleared I'll get the motor back together and double check the plug wires. I pulled the intake manifold thinking that the reed assembly for #1 cylinder may be stuck open. All reed assemblies look great and very clean. I'll reassemble with new reed assembly on #1 and then check out distributor again. I have a new cap, trigger rotor and will follow repair manual notes on filling cap wire towers 1/3 with OMC type C grease which I I understand is dialectic ignition grease. If all fails I'll get it to an expert with an ignition analyzer. Thanks for everyone's patience. I'm new to 2 cycle motors.

  14. #14
    Join Date
    Feb 2001
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    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Actually it doesn't make sense that installing a spark plug would make the engine run worse UNLESS that plug wire was screwed into the distributor cap at the wrong location... BUT... if that was the case, that means that at least one other spark plug wire would have to be screwed in to the distributor cap also... which in turn would make it an absolute truth that the engine would be running on two (2) cylinders.

    I see above that "Tim" has requested that you perform a compression test... In the trouble-shooting procedure, regardless of what the problem is, the first thing to do is to take a compression test, then a spark test, neither of which has been done yet according to the above.

    Remove all of the spark plugs, then do a compression test. What is the compression psi of all the individual cylinders.

    With the spark plugs still removed, do a spark test. On that model the "Air Gap" for the spark to jump should be set at 1/4" and should be a strong blue lightning like flame... a real SNAP!
    ********************
    (Spark Tester - Home Made)
    (J. Reeves)

    Most auto part stores have "air gap" spark testers... OR..........

    You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

    A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

    Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

    ..........X1..........X2

    .................X..(grd)

    ..........X3..........X4
    ********************
    Let us know what you find.
    We occasionally have questions. If you fail to answer, it may affect ours.

  15. #15

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    I am going through the distributor replacing the cap, trigger wheel (rotor sensor OMC part # 316459) and have located a rotor. I may replace all of the plug wires if I can find a new set at a reasonable price. Here's the question; the trigger wheel assembly uses 2 small pins identical size (about 1/8" x 3/16") that fit into the crankshaft to locate the trigger wheel. While the pins are identical the grooves on the bottom of the wheel they fit into are different one is wider. It seems one pin would be thicker. Why is this? As it stands now the wheel can go on in 2 positions 180 degrees different. It doesn't look like it would impact the firing. Is the larger groove simply to make installation easier? What am I missing? The Johnson 100ESL72 service manual doesn't give any details.

  16. #16
    Join Date
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    Duluth Mn
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    357

    Default Re: 72 Johnson 100 HP Ignition Problem 100ESL72R

    Have you done an accurate compression test? If not, all your expense and effort may be in vain. This motor is 45 years old, friend.

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