Troubled in Cincy (merc model 70)

Discussion in 'Outboards' started by rd9952, Sep 5, 2013.

  1. rd9952
    Joined: Sep 2013
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    Location: Cincinnati, Ohio

    rd9952 Junior Member

    I have a merc model 70 70hp outboard. Motor has new trigger, rebuilt fuel pump, new plugs, carbs have been rebuilt also. Motor needs help ( starter fluid ) to start and idles a little rough at low rpm's. Stalls out at min. throttle. When we put it in the water and try to shift it into gear it just stalls out or spits and sputters and then stops. ( dies out ) I am at my wits end. Any suggestions??
    Also stator checks good with an ohm meter per book.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    When the carbs were rebuilt, was all the varnish removed, or where they just sprayed with carb cleaner? If just sprayed down, the passages within the carb are likely partly clogged and still lined with a thin film of varnish. A thin film of varnish can change jet and needle sizes easily. You have to physically clean each orifice and passage and use lots of compressed air to blow out the debris.

    Timing would be another area to look. Is it dead on spec? Have you tried to advancing the timing a bit to get a good idle? What year is the 70 HP?
     
  3. rd9952
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    rd9952 Junior Member

    Troulbled in Cincy

    I haven't checked the timing yet. I used carb cleaner in every hole I could find on the carb. It has a little miss when idling and is hard to start. 1979 Mercury model 70
     
    Last edited: Sep 5, 2013
  4. rd9952
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    rd9952 Junior Member

    Troubled in Cincy

    Not sure how to check or advance the timing myself.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Sounds to me that the idle setting is too low at least, you should consult the manual to adjust that, which is likely a very simple screw adjustment. I would start having it at around 1100 rpm out of the water, in neutral, immersed in the water and in gear it will come down to 600-700 rpm, which is about the lower limit to avoid stalling. If it is too low you will conk out going into gear too easily, usually when you need the power the most ! If it is too high though, you will cause unnecessary wear and tear on gearbox components when going into gear. If this makes no difference to your problems it is another issue, but start with the simple fixes first.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Carb cleaner "in every hole" will not clean the carb, if it's moderately to heavily varnished up. The wisest and first thing you should do is by a book on the engine, which will cover the basic tuneup and diagnose procedures.

    [​IMG]

    This one is likely to cover your outboard and can be had for about $30 bucks.
     
  7. SamSam
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    SamSam Senior Member

    It's not easy to get three carburetors working right after taking them all apart.

    What does a new 'trigger' mean?
     
  8. rd9952
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    rd9952 Junior Member

    Thanks guys. I will try those sugesstions.
     
  9. SamSam
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    SamSam Senior Member

  10. Mr Efficiency
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    Mr Efficiency Senior Member

    I assume trigger refers to the CD ignition module.
     
  11. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    trigger is Merc's term for the sensor coils under the flywheel that move when you advance the throttle giving you advance.

    Make sure the choke is working if you have hard starting
     
  12. rd9952
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    rd9952 Junior Member

    Troubled in Cincy

    I checked the TDC and it was right on per the manual. When I crank it over with the plugs out the timing light still shows it just off the TDC setting. Shouldn't it be at a different degree point when cranking it at minimum throttle ? Is my timing off that much??
     
  13. rd9952
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    rd9952 Junior Member

    TDC is good per the O&M. But when I check it cranking at minimum throttle it is only slightly off the same TDC reading. ( 464 on the flywheel mark ) Could my timing be off that much or am I doing something wrong?
     
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It could be something as simple and synchronizing the carbs. You can run through the standard tune up procedures or use the hunt and peck routine. Most of us (that work on these regularly) will just go through a simple sequence of steps, looking for irregularities. We'll suspect some stuff and possibly get surprised by others, but usually in a just a few minutes we know which direction to focus, because something not right, be it timing, fuel delivery, electronics, whatever.

    As to specifics about this outboard, well what is it (make, model, year)? What are the current settings? Were the carbs actually rebuilt, or just sprayed with cleaner in a can and more importantly, where they adjusted after reinstallation. Are the tune up spec's "on the money", but you're still experiencing issues or are you just guessing?

    I'm not trying to insult you, but we need to know what you're working on and the current settings, just to have a level playing field. Do you own a service manual for this particular engine?
     

  15. Dave T
    Joined: Sep 2011
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    Dave T Senior Member

    Just bought a 1978 model 700 70 horse Merc and noticed this thread. If I have any problem with a motor the first thing I do is take a compression check. Most of the problems you're having sound like it could be low compression especially having to use ether to start when cold. If you have solved the problem please let us know what was wrong. I've noticed a lot of times on these threads people ask for help but you they usually don't say if their problem was solved. This could really help other people if they have the same problem.

    Dave T :)
     
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