Mercury outboard problems. HELP

Discussion in 'Bubba's Outboards' started by Localhero813, Aug 14, 2007.

  1. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    my 1968 marcury (merc)39 3.9 hp outboard is having problems. it will start and run for 10-20 seconds and then it will die . i wait a few minuets and try again and it does the same thing . the carb has been rebuilt and new needle valve installed. what am i missing?:sad2:
     
  2. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    Excues my badd typing its a mercury 3.9:sad2:
     

  3. ateamfisherman

    ateamfisherman New Member

    Messages:
    297
    State:
    Texas
    I had one fo them it did the samd thing itook it to shop they told me it had bad block. they said the compresson was low and ti would not pull the fuel into keep running.thats what they told me I let themhaveit for parts.thanks sam davis
     
  4. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    lots of little things can go wrong... a pinhole in the fuel line, soft lines that collapse, crap in the fuel lines which block the carbs... I would first run a compression check on the engine to see what it could be... don't have a compression tester...try your local auto zone... sometimes they will do the test free thinking you will buy spark plugs or other parts, or word of mouth advertisement of their store. Think I would do the compression test just to have a reference point... do one test dry then put about a teaspoon of oil in the plug hole and do a wet one. You should be fairly close on the readings... if your off quite a bit, you have bad rings or a bad cylinder wall. And at that, I don't think I'd trash the motor. You can pick up a ton of experience by trying to rebuild yours.
     
  5. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    Its to dang hot here in missouri to do anything(105*+). i replaced all the fuel line in the motor and i had it running earlier this year but i just cant figure out the problem:embarassed:
     
  6. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    You need to take that cotton pickin' coat off when it gets hot... unless your working a fire... I have scheduled all my work on boats and motors for the early morning hours (sun rise to about 10:00 AM) and the evening hours (7:30 PM to dark). Course I am retired so its no big deal if whatever it is don't get done today, tomorrow or next week. Eventually I'll run out of time...but I won't be around to care then...LOL

    I was running around this morning and went into the local Auto Zone store... just glancing at the stuff on the racks and low and behold... a spark plug tester for 7.39. I immediately bought one of them, because I think next to a compression tester these are one of the best things to have for an outboard motor. I had just bought a solid state plug tester from J.C. Whitney, regularly priced at 69.00 and it was on sale for 49.00. It is better than what I picked up today...but is not available all the time...I will keep this new tester in my boat...never can tell when I or someone else will need to know if they are getting spark or not.

    However, I got off the subject. Even in the heat of the day you can call a local parts store and see if they will run a compression check for you. As I have said, that is probably the first thing you should always do. I even record each cylinders' compression on a piece of white tape and tape it inside the cowling. I can always take another compression reading and somewhat tell what is happening within my motor.
     
  7. vegasryder

    vegasryder New Member

    Messages:
    324
    State:
    illinois
  8. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    went and tried to get it tested, but they did not have the right adaptor , but they said if i allready had it running that the compression should be ok he felt it with his thumb and said it was fine for a small 2 stroke. i tested the spark and it is good. the gas is brand new and i use it for my weed eater and it does fine( yes i know there is a big difference in the motors). i just dont know what else to do.
    from taking firefighter classes i know the fire triangle

    *
    fuel

    * *
    air ignition source

    i have fuel, i have an ignition source, and the carb is getting air. what am i missing?:angry:
     
  9. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    well mty triangle didnt work out but here is a pic.:wink:
     

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  10. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    There is a lower seal in the bottom of the crankcase that will cause the compression to fall out quickly and won't let it run long.
    What type of plug are you useing and I still can't phantom what type of adapter they would have needed to get that tester to fit the plug hole.

    Now don't take this personally but you can't test the compression with your thumb. All that does is tell you that the rings are indeed sealing against the wall some. Now on a down stroke it maybe not enough.
    Take you a squirt bottle and fill it with fuel mix and spray some in the carb while trying to start it and keep the choke closed while its trying to run to see if the fuel is getting to the plugs. Broken reed valves will do this also.
     
  11. vegasryder

    vegasryder New Member

    Messages:
    324
    State:
    illinois
    Just wondering...have you adjusted the needles prior to starting?
     
  12. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    well the reason that we could not use the compression tool would not work is that when we put the adaptor in the hole all the way tight the piston hits the tool.,but when we loosen ti so it dosent the air gets out:angry:
     
  13. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    also i didnt think about moving the valves i might try that this evening
    thanks:embarassed:
     
  14. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    im sorry i cant type tonite i will try thr needles tonite:confused2:
     
  15. vegasryder

    vegasryder New Member

    Messages:
    324
    State:
    illinois
    An easy fix for that is to add washers to the adapter.This will bring it up some so that the piston wont hit it.
     
  16. Localhero813

    Localhero813 New Member

    Messages:
    94
    State:
    Missouri
    yes but the washers wont seal aginst the motor
     
  17. vegasryder

    vegasryder New Member

    Messages:
    324
    State:
    illinois
    ^^^It`ll seal...I do it all the time with my small 2-stroke motors. Almost all the 39cc-50cc motors i mess with i try to raise the compression.The top of the pistons will always hit the compression testor.So to fix it, i would have to always add a washer or two so i can get a reading.