‘79 Johnson 25 hp

Home Forum Ask A Member ‘79 Johnson 25 hp

Viewing 10 posts - 11 through 20 (of 32 total)

  • Geer Pyron


    Replies: 139
    Topics: 47
    #251131

    I took the reed plate off. Two leaves on one of the reed valves were not seating properly. I could see light when I moved a light around the backside. Just a tiny sliver shown through in two places. My experience with reed valves is that when they are stuck open, bent or with debris, the motor will not start. Im skeptical that this is ultimately my problem, but it’s gonna get fixed.
    G

    JMGP


    billw

    US Member - 2 Years
    Replies: 2071
    Topics: 66
    #251163

    It was worth the look. I agree that if the reed’s just a little proud, that’s not your problem. I have seen them snapped right off on those engines. THAT’S a problem!

    Do you have neon, inline spark checkers to observe the spark action while running? Also, are you set up with a metal, pump-action oil can filled with two stroke mix gas, to squirt in the carb while under way? Those are useful test tools..

    Long live American manufacturing!


    Mumbles


    Replies: 5764
    Topics: 298
    #251167

    It sounds like you might be losing a cylinder under load. Since your carb and compression are good, it has to be something to do with the electrical system.

    Dropping a cylinder under load is one sign of a bad spark plug. Have you tried a set of new plugs? Erratic readings with the Tiny Tac could be caused by a weak spark on one cylinder. Try checking the spark plug wires from the plug terminal to ground and both coils should read fairly close. Also check the ground connections on both coils and the power pack for continuity and corrosion. I don’t have the specs handy but I can dig them out later. Also check the spring terminal under the plug boot for corrosion or poor contact with the wires core. They tend to come loose over time and can still show continuity and produce a good spark while testing but can’t supply enough juice to fire the plug while the motor is under load. If wiggling the terminal while hooked up to the ohm meter causes the reading to bounce around, then you know the spring terminal connection is bad.

    • This reply was modified 2 years, 3 months ago by Mumbles.

    fleetwin

    US Member - 2 Years
    Replies: 4737
    Topics: 46
    #251173

    Is this engine new to you, or have you owned it for awhile? If you have owned it, when was the last time it ran OK at high speeds.. I just want to review the symptoms: seems to run fine at low speeds, but lacks power at WOT, but does not miss/skip/misfire…. Do I have it right?
    Sounds like you have checked sync/economizer linkage, and the timing is advancing fully against its rubber stop, and the economizer linkage is pushing the carb butterfly open fully. You are running the engine on a boat with a prop at WOT, which is how you are testing it? If so, what pitch prop do you have and what type/length boat is the engine on?
    Try to avoid getting in too deep, or spending money on a powerpack unless you can confirm the engine is misfiring/losing spark. I suppose it is possible that the engine is just running on one cylinder, but you would have noticed a poor idle…I suppose it is also possible that the engine is “dropping a cylinder” at WOT, but I would think you would hear it drop out.
    I am confused by your tach readings, so am not paying too much attention to that right now. Again, sometimes test equipment can be our worst enemy which causes us to make improper conclusions based on inaccurate test results.


    Geer Pyron


    Replies: 139
    Topics: 47
    #251183

    I’ve reread all the replies a few times now. I have a plan.
    But to answer a few questions, I do not have a neon in line spark tester, but will order one right after Christmas. But I do have a nifty little squirt bottle that I use. It sure beats doing the Mad Max Fury Road war boys tactic!
    I run my bigger motors, over 10 hp, on a 16’ 1973 Loweline. Sometimes with Hank, mostly just me gas and small tool box. No dog. The boat is a good running boat. A Scott Atwater 7.5 hp planes it! It books with my ‘04 merc 25.
    I’ve put a different prop on the motor in question. I got the motor recently for very little. It came with a 10 1/4” x 11 prop. I only thought about the prop when I happened to notice how little clearance there was between blade and water pick up.
    I jacked a 9 1/4” x 11 from another motor.
    And yes, it idles good as far as I can tell and lacks power at wot. Weather it is dropping a cylinder or not is beyond my expertise. I simply can’t tell. That’s why I hooked the tach up. But that was dumb because I never ran it wot with the tach hooked up.
    I’m going to put intake manifold back together and focus on the electrical aspect. Hanks words are ringing in my ears, “Whaaaaaa???? You didn’t get new plugs??? They are 3 bucks!!!”
    A lot, if not all, of the ground connections have been re done by me. Just in the course of taking things apart and putting them back together.
    But I’ll check everything that has been suggested, plug booties back To the mag.
    And dispite really wanting to use the tachometer and buy one(or two) for every motor I have, I’m going to back away. I can still see Mr. Woods cocking his head, touching the top of a running motor and saying, “Oh, you put new rings in it. That noise will go away by the time we get back to the dock” It did. And I had said nothing about putting new rings in, which I had.
    It’ll be a few days till I can get back to it but I’ll keep y’all posted.
    I hope it all works out. I’ve already found a guy who will keep it at his lake house on a boat and let me use it, and fix it, whenever I want!
    Thank you all for the input.
    G

    JMGP


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #251187

    sorry to ask but you would not have one of these….would you ?

    Joining AOMCI has priviledges 🙂


    Geer Pyron


    Replies: 139
    Topics: 47
    #251193

    Ha!
    The multimeter.
    Bane of my existence.
    I have several. None of which I know how to use. Except maybe the one with the needle.
    Learning how to use it, really use it, is on my list of things to do.
    As of right now I feel like I am just transcribing Arabic when I use it. I can write the Koran, but not know a single word. With the multimeter I simply do what the picture says. Know what I mean?
    I do have enough of a grasp to at least be able to tell if a ground wire isn’t making good contact, or a plug wire is broken where I can’t see it.
    I was up late last night using it to check things out.
    Thanks for having my back.
    G

    JMGP


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #251194

    actually… I was alluding to the broken wire. 🙂

    as for meter just go on the x1 scale… you should see a steady 0 ohms from boot to engine frame (scrape the paint off!!) wiggle the wire and twist the throttle from STOP to FAST while testing the wires. the reading should hold steady around 0 ohms

    http://www.pochefamily.org/outboard/Coils.htm testing coils is much like testing any resistance and it is a needle meter 🙂

    remember UTUBE is your friend.. most of the time

    Joining AOMCI has priviledges 🙂

    • This reply was modified 2 years, 3 months ago by crosbyman.

    Geer Pyron


    Replies: 139
    Topics: 47
    #251250

    Ha! That was funny. I really did think you were asking if I had a multimeter.
    But hey!!! I think I found the culprit.
    Fingers crossed, and maybe I shouldn’t say anything lest I jinx myself, but I’m confident.
    I took the motor out this morning after re adjusting economizer link, going through the electrical stuff, and putting n brand new L78V plugs.
    No change. Same problem.
    But this time The Hank was with me and he insisted the motor was running to rich, like when you first put an old motor in the water and have to tweak that high speed needle before installing air box. It was just sluggish and I wished I had a high speed adjustment needle.
    But alas, it is fixed jet in this motor.
    But, since I skipped work today, I took the jet out of another 25 hp omc.
    And compared them.
    Noticibly different origice sizes.
    I’m thinking some one had stuck the larger 35 hp hs jet in the smaller throated 25 hp carb in an attempt to convert it but didn’t take out the plastic air restrictor in the throat. More gas sure, but not more air.
    I’m off to the lake!
    G

    JMGP


    fleetwin

    US Member - 2 Years
    Replies: 4737
    Topics: 46
    #251251

    Good investigative work for sure!

Viewing 10 posts - 11 through 20 (of 32 total)
  • You must be logged in to reply to this topic.