Weak spark on 1973 20 Hp Johnson

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    fleetwin

    US Member - 2 Years
    Replies: 3598
    Topics: 35
    #210350

    Yes, the bowls are the same, except for the high speed jet, but the bodies are different…
    Did you check to see if the choke is staying fully closed while cranking? Are you advancing the throttle to its stop in neutral? It is not going to start easily at dead idle when cold..

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    reivertom

    US Member - 2 Years
    Replies: 695
    Topics: 36
    #210363

    Yes, I remember you posting about the new coils. But, Mumbles post is a good reminder for the rest of us when checking coil secondary resistance. Those poor/rusted connections often show up as an infinite resistance reading on the high ohms scale…A good coil could be discarded only because of a poor/rusted plug boot/terminal…

    If you don’t mind, could you tell me what years this type ignition was in use? I am looking for a similar size OMC motor, and would rather avoid them.

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    fleetwin

    US Member - 2 Years
    Replies: 3598
    Topics: 35
    #210374

    This low tension system was used on some engines from 1973 thru 1976, and a few more years later on some commercial models…. It is best to be able to recognize the system when you see it though only because model years are often misrepresented/unknown on used engines.

    1 user thanked author for this post.
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    Evinrude 25


    Replies: 81
    Topics: 11
    #210392

    Hello,
    Rusted or poor terminal connection rules out in this case since the spare plug cable comes together with the coil as you could see in the picture. It is Mallory Marine Ignition Coil 9-23106. I have checked the new coil resistance vs the old coil. I don’t see the different. I suspect the old coil is still good. I am going to put the old coil back to see if I could get the spark!!! It is just an experiment.

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    GLEN DEUTSCH

    US Member - 2 Years
    Replies: 37
    Topics: 18
    #210399

    Evinrude 25

    Can’t over emphasize the importance of that thin round plastic bearing under the mag plate. I fiddled for two months thinking that a little crack in the plastic and a little wobble would not hurt. Could not get it running. Frustrated. Finally, replaced the ring and it runs great.

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    Evinrude 25


    Replies: 81
    Topics: 11
    #210400

    Other point I read in other post about the point setup gap. I setup 0.020 on both points (New OEM OMC) I found out one side was Ok to set the gap more than 0.02″ but other point I barely got less than 0.020″. Then I used the Ohm meter method to find the correct timing. That point was just made it at the very maximum opening adjustment. The adjustment screw turned at max. Why??? Manufacturing inconsistencies??? Or the wear out of the plate bearing?

    • This reply was modified 5 months, 3 weeks ago by AvatarEvinrude 25.
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    fleetwin

    US Member - 2 Years
    Replies: 3598
    Topics: 35
    #210447

    Evinrude 25

    Can’t over emphasize the importance of that thin round plastic bearing under the mag plate. I fiddled for two months thinking that a little crack in the plastic and a little wobble would not hurt. Could not get it running. Frustrated. Finally, replaced the ring and it runs great.

    The 20hp did not use the plastic bushing, it still had the conventional brass ring and aluminum retainer set up…
    But, you make an excellent point. Those plastic bushings should be considered throw away parts and replaced during every servicing, just like gaskets…

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    fleetwin

    US Member - 2 Years
    Replies: 3598
    Topics: 35
    #210448

    Hello,
    Rusted or poor terminal connection rules out in this case since the spare plug cable comes together with the coil as you could see in the picture. It is Mallory Marine Ignition Coil 9-23106. I have checked the new coil resistance vs the old coil. I don’t see the different. I suspect the old coil is still good. I am going to put the old coil back to see if I could get the spark!!! It is just an experiment.

    I don’t think you have an ignition problem, the engine sparks well while cranking, correct? Have you checked the choke linkage?

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    Evinrude 25


    Replies: 81
    Topics: 11
    #210536

    Yes, it has spark. Now I need to focus on the carb.

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    RANDY SCHNEIDER

    US Member - 2 Years
    Replies: 5
    Topics: 0
    #210570

    I may be all wet, but I thought the carbs on those had a plastic low speed needle jet seat. Im pretty sure I bought one from Ed for a 20 I had to work on a while back. Seems they can get smashed or crack. I had to use a straightened fish hook to snag it out. Its a distant memory, but I remember fising that bushing and gettting the plate flat again. Might be something,
    Randy

    Mumbles
    Mumbles

    Canada Member - 2 Years
    Replies: 4642
    Topics: 259
    #210571

    I may be all wet, but I thought the carbs on those had a plastic low speed needle jet seat. Im pretty sure I bought one from Ed for a 20 I had to work on a while back. Seems they can get smashed or crack. I had to use a straightened fish hook to snag it out. Its a distant memory, but I remember fising that bushing and gettting the plate flat again. Might be something,
    Randy

    These carbs have a small plastic bearing/seal deep inside them for the low speed needle. A new one will be included in a carb kit.

    Carb-Bearing-Tool

    • This reply was modified 5 months, 3 weeks ago by MumblesMumbles.
    • This reply was modified 5 months, 3 weeks ago by MumblesMumbles.
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    Evinrude 25


    Replies: 81
    Topics: 11
    #211023

    Hello,
    I am back to the board again! after cleaning the carb and put it back. I could start it 2 times. It ran ok since I by passed the kill switch. I could not stop it by the choke. I had to unplug the spark plug cable of the first cylinder to kill the engine while the choke still engaged. The engine was not stopped right away. It was still ran for a couple seconds. I started it again and un-pluged the second cylinder spark plug. It stopped right away. Next day, I could not get it run. Both cylinder still had spark. Pull many, many times until I broke the recoil spring so I could not start it. The recoil spring broke at the end so I could be able to rivet it back but have not done yet. Try to figure out how to adjust it.

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    fleetwin

    US Member - 2 Years
    Replies: 3598
    Topics: 35
    #211033

    OK, you are losing me here. Are you saying the engine will not shut off when you press the stop button? What do you mean by “passed the kill switch”??
    The engine may not shut off when you pull the choke because the choke is set up to release a bit when it starts so it won’t flood and stall.
    I fear you are getting a bit confused….
    I want to review your initial issue…I thought you said the engine was tough to start when cold, but ran OK once started…And started OK when hot.
    I suggested you check to make sure the choke was closing fully while cranking, you reported pulling the carburetor apart….
    Did you check to see if the choke was closing fully while cranking?
    This choke linkage is a little complex…It was engineered so that the choke would pop open slightly once started so it won’t flood and stall easily. You will also notice that the choke linkage opens the carb butterfly a bit when engaged also to make cold starting a little easier… So, if the linkage is messed up causing the choke not to close fully while cranking, or if it is not opening the butterfly slightly when engaged, it will be tough to start cold….

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    Evinrude 25


    Replies: 81
    Topics: 11
    #211067

    I have by-passed the kill switch (remove the wire of the stop button from the coil) during the process to make sure that I have spark on both cylinders. I forgot to connect again so when I ran the motor. I could not stop it by pressing the stop button. So I tried to choke it in order to shut it down but it did not so I had to pull the spark plug wire.
    Yes, it is very hard to start at cold start! Even though I had the choke fully closing. I saw the saw flood out sometime. I will review of what you said and check all the linkage.
    Timing of the point also had been rechecked to make sure the point open when the flywheel mark lined up between two mark on the mag plate.I put the new driver coil in so the whole ignition system has completely new part and it has strong spark!

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    fleetwin

    US Member - 2 Years
    Replies: 3598
    Topics: 35
    #211069

    Did the stop switch work before you disconnected it? If so, I can’t imagine why it wouldn’t work now…I don’t think there is a way to connect it improperly, there would be no spark if you inadvertently connected the stop leads to the coil primary connections. It is easy enough to check the stop switch leads with an ohm meter…
    Using an ohmmeter on the high scale, connect the leads to the disconnected stop switch leads….The meter should read infinity, nothing less…
    Using an ohmmeter on the low scale, connect the leads to the disconnected stop switch leads with the stop button depressed….The meter should read near zero ohms.
    You report there is good spark, and that you are holding the choke closed….
    Is the throttle advance linkage hooked up to the choke? Are you advancing the throttle sufficiently?

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