1979 Merc won't throttle-up

Discussion in 'Gas Engines' started by JEH63, Sep 7, 2018.

  1. JEH63
    Joined: Sep 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Boise

    JEH63 Junior Member

    Have an odd situation with a 1979 Mercury 70hp outboard. Buddy gave me the boat. Had been sitting for 8 years. I went through the motor. Replaced stator, rectifier, all fuel lines, rebuilt fuel pump, gasket kit and cleaned the carbs, replaced fuel filter, replaces plugs, installed new wiring, new tank and primer bulb. Take the boat out and it ran like a scalded dog for a mile or so. Shut it down and turned off for @ 10 minutes. Restarted and it just bogged down. Wouldn't even cruise at 10 mph. Tried opening the lid on the tank, pumping bulb, and even switched tanks...still wouldn't go. Idles fine and you can put in neutral and use the warm-up throttle and it'll attain a high rpm. Thinking maybe stuck float in one of the carbs? Would like to hear any input any of you may have. I'm a bit confused with this one...
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,632
    Likes: 252, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    You say you tried pumping the primer bulb ? That should have "unstuck" a carby float or needle valve, at least temporarily. It could be some debris has lodged in the main jet of one card. It sounds as if you are running on 2 of the three cylinders, it might not be fuel, maybe a coil has died. You should get hold of a workshop manual, and consult troubleshooting procedures, and test all ignition components with a multimeter.
     
  3. JEH63
    Joined: Sep 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Boise

    JEH63 Junior Member

    Thanks for your quick reply. I’ll certainly look at that. Just confusing because it ran so well until I shut it down. I do have a manual so I guess I have something to do this weekend.
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,632
    Likes: 252, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Did you replace the coils, as well as those other ignition parts ? I got hold of an old 4 cylinder engine one time, noticed that one of the coils was dead ( it was hard to start) replaced it, ran the engine on a boat, it went well for ten minutes, then dropped a cylinder, and lost speed badly. The cause was a faulty plug lead, if the circuit to the plug fails, the coil will be destroyed pretty quickly.
     
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  5. JEH63
    Joined: Sep 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Boise

    JEH63 Junior Member

    I have not. But this will be the first place I check next. Thanks again...I have the manual and need to go through everything, I suppose. Check timing, compression, etc. One thing I should have mentioned...when I replaced the stator, the wires were too short on the new one to orient it the way the original was and still connect the wires to the control box. I read a few place on-line where you can offset the orientation by 60 degrees and no problems. Seems like a valid approach since the bolt holes on the stator exactly line up on 60 degree increments. Anyway...thanks so much for your time. If nothing else, I sure am learning a lot about old outboards! Have yourself a great weekend!
     
  6. JEH63
    Joined: Sep 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Boise

    JEH63 Junior Member

    Just measured resistance in the coils. About .2 ohms each. I pulled the two lines coming from a cylinder to the fuel pump. One of them had a little water in it. Don't think that's good. Need to find out how that can happen. I'm thinking it may be the cause of the fuel pump operating poorly.
     

  7. JEH63
    Joined: Sep 2018
    Posts: 5
    Likes: 0, Points: 1
    Location: Boise

    JEH63 Junior Member

    Just took apart the carbs again. Found a potential issue. Appears like the main jet was swapped with the other jet on the carb. Looked at the specs for each...main jet is .086 and the other is .066 Could be what's causing fuel issues with the lower. Ordering new floats, needles and seats. Got my fingers crossed!
     
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