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Results 1 to 23 of 23
  1. #1

    Default 1980 mercury 70 hp 3cyc will not open up

    hello, I have a 1980 mercury 70hp 3 cyc that will not rev over 2000 rpm. I replaced the stator and voltage regulator last month and still wont accelerate above 2000. Does any one know if the trigger has a low side and high side or does the switch box??? This engine starts easy choke one time then just turn the key the rest of the time.

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,417

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Question: Does it rev right up in neutral?

    Jeff (triple expert)

  3. #3

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    yes just fine. thats what is puzzling, but under a load no. This motor would run 30mph on my boat then the stator went out now it runs 14 mph.

  4. #4
    Join Date
    Sep 2010
    Location
    ontario
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Do a compression test and check spark to see if it jumps a gap of 7/16" on all 3 cylinders.

  5. #5
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    618

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Also check that the trigger is advancing and both carbs are opening up when throttle is opened (not running please)

  6. #6

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    ok did a compression check 128 top 131 middle 123 bottom and good blue spark. I accidently fired it off I was showing my son what to do and it fired off. How would I see if the trigger is advancing? And one more thing someone told me of you replace the stator you have to replace the trigger? I am new to mercurys and this newer ignition I had a evinrude that had points. thanks for all the info.

  7. #7
    Join Date
    Sep 2003
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    The stator and trigger are unrelated when one of them fails, but your stator is suspect: if it's screwed up, the motor won't run right since IT produces the 300 volts to run the ignition system (as well as charging the battery).

    The trigger coil is moved by that linkage atop the throttle arm on the left side.

    Now, back to your problem: bogging on accelerating. I experienced this on mine and TOTALLY cured it by modifying the carbs. Not hard to do if you're handy with tools. The carbs have to come off and the existing holes in the butterflies drilled out to 1/8 inch (all three per carb). That's all it takes and the bog is outta there! Oh, and add a bit more idle mixture (turn the mixture screws CCW about 1/2 turn) to compensate for that crappy ethanol gas.

    Jeff
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    Last edited by fastjeff; 03-23-2012 at 07:01 AM.

  8. #8
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    618

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    I read nowhere in post about it bogging??? Since you changed the stator was it new or used? Was it the 9 amp stator? It is possible if it was a used stator and wrong amp the stator laminations could be thinner causing the stator mounting screw to protrude keeping trigger from fully rotating. I have seen this several times on I-6 engine going from a 16 to a 9 amp stator. Dont do anything to the carbs till you rule out everthing else...

  9. #9

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    ok did an extensive look at this engine. 1. pulled the flywheel nothing touching the stator is a 9 amp and it is new cdi brand. 2. examined trigger its kinda loose and I am not sure if they are suppose to wiggle or what. 3. ohm the trigger and its in the 900 range. 4. put flywheel back on. 5. looked for throttle travel it is exactally where it is suppose to be. 6. turned the key and about less than 2 seconds it fired up. so i am thinking that the trigger and switchbox and coils will be replaced over the next few weeks. I am thinking new parts will be better in the long run. I will also get new fuel pump and water pump.

  10. #10
    Join Date
    Sep 2010
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    ontario
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Sounds like an expensive way to look for the problem.-----------------Maybe all you have is some dirt / blockage in a carburetor.-----Or a reed valve / crankcase compression problem----------Or a ruptured diaphragm in the fuel pump.----Or a bad float valve in one of the carburetors and pouring too much fuel into the engine.

  11. #11
    Join Date
    Sep 2003
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    New Tripoli, PA, USA!
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    I seriously doubt there's anything wrong with the stator or trigger coil (and it's supposed to be loose like that). Since the motor starts and idles reasonably well, revs right up in neutra,l but won't take throttle in gear, the carbs are either in need of a good cleaning, or they need the modification I recommended above (that has worked great on my two 70 hp Mercs).

    It's your choice.

    Jeff

  12. #12
    Join Date
    Apr 2010
    Location
    Richmond, Va
    Posts
    7

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Have to agree with racerone & fastjeff, before you replace electronics make SURE there are no carb problems. It took me 3 times to remove carbs before finding a small piece of trash ( using a magnifying glass ).

  13. #13

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    I have found some trash in the tank and have ordered a fuel pump kit. Ok i was messin with the tanks pick up tube and i dropped it in the tank. OMG what a dummy i am do you know that it is impossible to "fish" out a tube. So now i am heading to lowes or somewhere to find a tube. If i am guessing it may have a filter on the end. It is a 10 gallon inboard tank.

  14. #14
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,293

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Use remote mechanical fingers found in most auto parts stores.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  15. #15

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    ok got a better tube in the hole and the flow is awesome. now need a fuel pump kit and carb cleaner i am going to eliminate the fuel questions

  16. #16

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    OK heres what I did this week 1.rebuilt fuel pump. 2. put a inline filter on the line 3.cleaned the carbs 4.ran 10 gallons which 5 had seafoam in it. It is opening up but missing bad so i adjusted the timing and it got worse so put back where it was. I hate mercurys they are so complicated geez I am trying to like it but it looks like the trigger and switch box and coils and if that doesnt fix it I will sell it and get a evinrude.

  17. #17
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    Sep 2003
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Have you done a compression test, especially on the top cyllinder?

    Jeff

  18. #18
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    see post #6

    I'm betting some of the trash in the fuel tank is in the carbs.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  19. #19

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    top 125 mid 122 bottom 124 and cleaned the carbs. its a missin only when its wide open i am thinkin the trigger needs replacing then the switch box then the coils. then its a new motor and should run right.....right?

  20. #20
    Join Date
    Aug 2006
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    SW Ohio, USA
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Another boater boater had an engine miss and did a leakdown test and found a problem. He opened the engine and found an internal crack.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  21. #21
    Join Date
    Sep 2010
    Location
    ontario
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    Put a timing light on it and see if it is an ignition miss.--------------Testing and trouble shooting is the way to move forward.

  22. #22
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    Sep 2003
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    Default Re: 1980 mercury 70 hp 3cyc will not open up

    One more thing you can try--and it's an easy one: Mine also had a high speed miss and it was caused by two of those black caps that cover the screws on terminals on the spark box not being all the way on. The stator develops up to 300 volts, so those caps must all be on tight or the voltage will jump to another terminal.

    Be sure there all on tight!

    Jeff

  23. #23

    Default Re: 1980 mercury 70 hp 3cyc will not open up

    well took it out this weekend and it ran much better and the only thing that I did was wiggled wires and put gas in it. I am going to replace foot seals and water pump.

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