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  1. #1
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    Fitting later model ignition system to 1975 Johnson 115

    Probably a stupid question but here goes. I have a no spark 1975 Johnson 115. I can get a parts motor 1981 Evinrude 90hp (seized) for pretty cheap. I know there is limited compatible parts between these models. The ignition system components - stator, trigger, coils, powerpack are all different part numbers to my 1975 Johnson 115. The flywheel is different. I have already found my stator is out of spec (reading 624ohms - upper limit seems to be 600ohms). Possibly other ignition parts will need replacing as haven't finished testing yet and I believe triggers often go on these.

    If the later model's ignition parts all tested ok, would it be possible (and advisable) to replace all of the ignition components including flywheel?

    P.s. on a semi-related topic, there was a previous suggestion that you can fit digital ignition to these old motors. I contacted CDI and they only do those kits for V6 loopers apparently.

  2. #2
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    i dont remember to much about that year but it was a pretty good ignition system they had 2 power packs v4 the replacement stators were really good we had a few power packs go bad other than that were good good thing you always had 2 cylinders running to get you home jim45157

  3. #3
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    Yes your right it appears that the 1980 model 90hp does have 2 power packs versus 1 in my 1975 model. Question is will the system fit and work as intended? With all the tinkerers on here I figure someone has tried at some point. Apart from whether it all fits and works, I can imagine that the flywheel might be a different weight which might be an issue. I did also read somewhere that "the crank and flywheel are a MATCHED SET from the factory and seat themselves uniquely".
    Last edited by Gilera; 11-30-2021 at 08:21 PM.

  4. #4
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    cant see why it wouldnt work. You will need to make coil mounts or get later heads.
    Check the crankcase top bearing housing to see if its the same number on both engines.
    Last edited by powerabout; 11-30-2021 at 09:36 PM.

  5. #5
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    I have been waiting for a puller to arrive in the post so I can remove the flywheel but from what I can see the electrics do look pretty good on this seized 1980 model 85hp. Apart from mounting the coils, it also looks like i'd have to find a place for the power packs as the later block has fixing point for these molded in the block.

    I was also looking at the possibility of changing over the airbox to this later version as mine is missing the cover. It looks like this would involve changing to the fuel primer too as the choke solenoid mounts on the side of my current airbox. Fuel pump mounting and design also slightly different.

    My choke solenoid operates fine in that it closes the butterflies when pushing the key in. I have never owned one of these motors before. The primer setup is quite a bit more complicated and I would also need to find somewhere to mount the solenoid.

    Is the primer setup much of an improvement in terms of ease of starting over the traditional choke setup? I live in a tropical climate - no super cold starts.

    Does it matter much if my airbox is missing the cover? I have heard they are a lot louder without the cover and also that fuel runs back out of the carbs into the cover when the motor is tilted up.

  6. #6
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    I finally got to take the flywheel off my 1975 Johnson 115 last night. Before I took it off I could not get any DVA reading from any of the trigger wires to ground so am assuming the trigger is bad. Disconnecting them from the power pack didn’t change this. What would cause no reading at all?

    I can see where one of the two ?sensors on the inside of the trigger has been replaced previously – see photo. The screws are different and the paint over the nut on the outside was all scratched up. Would replacing these sensors again maybe fix it?

    The stator has a few dark areas where the resin has globs on it – see photos. I’m guessing these are signs of wear and wondering whether it would also need replacement. Resistance was a bit high at 624ohms but DVA output was good before I took it off (260V).

    Coils are cracked but specs were ok. I have a spare set of the green coils that came with the motor but one of them has very high resistance reading on the secondary measurement.

    I also took the flywheel off the 1980 model Johnson 85hp (which was sold to me as a 1981 Evinrude 90hp by a large local Marine mechanic workshop!).

    The stator on it looks in decent condition (original). The trigger is a CDI replacement as looks very clean. One of the power packs is CDI and the other original. Coils are original and specs are ok except one has a higher reading on the primary (3.8ohms vs 0.6ohms for the other three.

    If I am up for a new trigger, possibly stator and coils this would be over $1000AUD for CDI brand. That is assuming power pack is ok which I wouldn’t know for sure until I replaced trigger.

    This would be enough motivation to try swapping over the ignition system from the later model.

    Looking over the newer model carefully, I now realize that quite a lot of parts are mounted in different locations (you all probably knew this already).

    I think the easiest way to do it would be to keep the existing terminal block and rectifier on the '75 model and get the yellow wire form the staor to the terminal block. Then make mounts for the coils and power packs in a location where the wires will reach. I’d probably also add the regulator from the later model and the '75 model doesn’t have one.

    Any suggestions on what to make the mounts out of? Easiest options for me would be aluminium angle bolted together or mild steel welded and painted with zinc.

    I could replace the heads with the ones from the ’80 model but this motor was seized due to water in cylinders and I don’t know what condition they are in. Also probably just as much hassle replacing them then making mounts.

    Is it necessary to lap the flywheel on these motors to ensure a perfect mating surface?

    Any advice is appreciated.

    Click image for larger version. 

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    Last edited by Gilera; 12-14-2021 at 08:41 PM. Reason: typo

  7. #7
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    Make brackets from the water jacket cover bolts on the heads for your coils.
    I will post a photo but something not working on the site atm.

    You dont need to lap the flywheel if both surfaces look good.
    Just drop it on and see if you can pull it back off, if it sticks its a good match.

    Toasted stators mostly come from using non lead acid battery and or loose terminals.

    Sensor wires dont go to ground when you have 2 sensor coils and 4 cylinders to fire.
    Last edited by powerabout; 12-14-2021 at 09:43 PM.

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    Quote Originally Posted by powerabout View Post
    Make brackets from the water jacket cover bolts on the heads for your coils.
    I will post a photo but something not working on the site atm.

    You dont need to lap the flywheel if both surfaces look good.
    Just drop it on and see if you can pull it back off, if it sticks its a good match.

    Toasted stators mostly come from using non lead acid battery and or loose terminals.

    Sensor wires dont go to ground when you have 2 sensor coils and 4 cylinders to fire.
    Thank you!

    When I was talking about the sensor wires, I was following the following troubleshooting directions:

    Check the DVA voltage on each black/white wire to engine ground. You should have a reading of at least 150V or more (while connected to the pack). If the reading is low, disconnect the trigger wires from the pack and recheck the black/white terminals on the pack. If the voltage jumps up to an acceptable reading, the timer base may have a problem in the internal wiring (A thin spot in the insulation on one wire).

  9. #9
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    Quote Originally Posted by Gilera View Post
    Thank you!

    When I was talking about the sensor wires, I was following the following troubleshooting directions:

    Check the DVA voltage on each black/white wire to engine ground. You should have a reading of at least 150V or more (while connected to the pack). If the reading is low, disconnect the trigger wires from the pack and recheck the black/white terminals on the pack. If the voltage jumps up to an acceptable reading, the timer base may have a problem in the internal wiring (A thin spot in the insulation on one wire).
    sensor voltage is under 1.0 volt ( peak)
    Whose troubleshooting guide is that?
    150v plus is charge coil voltage from the stator

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  11. #11
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    I only have a homemade DVA voltage adapter which has a diode in it so I didn't think I would be able to do the low voltage measurement with any accuracy.

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    Quote Originally Posted by Gilera View Post
    yes it says black white to black white 0.6v
    Just have to make sure you go between 1 and 3 ( one sensor coil)
    then 2 and 4 ( other sensor coil)

  13. #13
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    I would need a much better multimeter to measure that.
    I also measured the resistances which are supposed to be 10-20ohms.
    I got:
    Sensor 1 to 3 : 8.2 ohms
    Sensor 2 to 4 : 8.0 ohms

  14. #14
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    Quote Originally Posted by Gilera View Post
    I would need a much better multimeter to measure that.
    I also measured the resistances which are supposed to be 10-20ohms.
    I got:
    Sensor 1 to 3 : 8.2 ohms
    Sensor 2 to 4 : 8.0 ohms
    resistance checks for me are just preliminary to see if open circuit.
    its the voltage that counts

  15. #15
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    I went out and bought a better multimeter yesterday which can measure AC voltage in mV range and has max and hold functions. I'll put the '75 model ignition system back together and see if I can troubleshoot more accurately this time.

    I will still probably change the system over though unless my no spark issue turns out to be something simple. Powerabout, if you can upload a photo of a mounting suggestion at some point i'd really appreciate it.

    As far as compatibility of the bearing carrier, there was no numbers written on the older motor. But I looked up the part number for "Crankcase Head and Bearing Assy" and the part numbers are the same for both motors. The top of the assembly does look different between the motors though - there is an angled shoulder on the newer motor whereas it is squared off on the older one - see photos. I assume it should still work?

    I worked out that I should be able to use my original harness and just relocate the kill wire from the terminal style powerpack on the 75' model to an unused position on the terminal block (looks like it will reach ok). If I unravel the harness from the newer motor and take the kill wire that goes to both plugs for the power packs and also connect it to this same position on the terminal block it should just require the mounts for newer packs and coils and take off old pack and coil assembly. Easy to change back if it doesn't work!

    Older crank:
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    Newer crank:
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