2004 9.9 mercury 2-stroke half power

Discussion in 'Outboards' started by kenrahe, Apr 18, 2010.

  1. kenrahe
    Joined: Apr 2010
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    Location: pomfret ct

    kenrahe Sunseeker

    2004 9.9 mercury half power

    my top cylinder is not firing,i have spark, 120 psi.compression in top and bottom cylinders..did fire for a little bit after compression check,then stopped agian,is this a carburator problem.if not what else can i check.
     
  2. kenrahe
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    kenrahe Sunseeker

    sorry forgot to mention that
     
  3. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    I assume you have checked it with the plug out of the cylinder ...it needs more volts under pressure ..try reducing the gap a bit .. 120 sounds very high ..did you put oil in it ..if so thats a false reading normally about 60-80 on a two stroke ..I would try some easy start down the carb and get the carb cleaned out dismantle and blow with compressed air...good to soak in thinner overnight to clean it up...could be the fuel pump ...faulty reed valve for that cyliner .how long has it not run for ???
     
  4. kenrahe
    Joined: Apr 2010
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    kenrahe Sunseeker

    no i did not put oil in it ran last season, bought off my boss but he's in fla. right now ,i used a auto compression gauge not sure if that mattered .how hard is it to check reed valve an do you have the way to check.and is it a big job to take off carb i have an wellcraft aft cabin that i do all the work on an this motor was to have a better dingy motor for my wife to go to shore with that was easy for her to operate
     
  5. SaltOntheBrain
    Joined: Feb 2007
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    SaltOntheBrain Senior Member

    When you check compression, do it with the throttle closed.

    Count strokes from start to max pressure and compare both cylinders.

    Start the engine in complete darkness and look for electricity crawling over the spark plug wires. Does it run better ith the cowl off? The cowl may push a wire too close to something that could short it out.

    These are problems I ran into with an old Tohatsu I used to run.

    Let us know when you get it nailed.

    Lance.
     
  6. capt littlelegs
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    capt littlelegs New Member

    Change the plugs.
     
  7. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    Usually when one cylinder goes out one assumes that CDI, fuel is at fault. If Im not mistaken your little Merc has a single carburetor and since one cylinder runs the other should as well - that eliminates fuel supply. Check for stuck reed valve.
    If that is also OK, spark should be the culprit...

    We service many a Yamaha motors - mostly 85hp - that is as South African as a Hilux bakkie here ;) and usually when one cylinder spark goes on the blink (most of the time after a few seconds to a minute running), they come long face about the CDI that's gone and these critters cost a fortune here.
    It is rare for a CDI unit to loose spark only on one cylinder - all will be out. Usually the culprit it the small pickup coils under the flywheel that sends a signal to the CDI. It can be easily be checked with a multi meter, just measure the resistance in each coil and if one is way out, replace. I believe this is the problem with your little Merc.

    Your compression is spot-on for a well looked to new engine.
     
  8. Knut Sand
    Joined: Apr 2003
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    Knut Sand Senior Member


    Exactly what happened to mine...(Marineer) Got hand on some used part, replaced last summer, now its good as new. It even drowned this winter (freshwater/ river, close to the sea) The boat was screwed down by the ice... Got it up a couple of weeks ago, drained (_all_ of) it filled it with ethanol, let it rest for a couple of days (ethanol inside), drained again, pressurized air, pulling, good spark (!), gas and start gas, dont think I had more pulls than 4-6, then it was running nicely, just got lucky I guess...
     
  9. kenrahe
    Joined: Apr 2010
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    kenrahe Sunseeker

    thanks alot

    thanks for your help i'll try all tonignt an keep informed
     
  10. kenrahe
    Joined: Apr 2010
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    Location: pomfret ct

    kenrahe Sunseeker

    put in brand new plugs to motor recmondation ngkbp8hs
     
  11. capt littlelegs
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    capt littlelegs New Member

    Yep, the most common outboard problem is plugs and the cheapest to try first. Check the cap is fitting properly as well.
     
  12. kenrahe
    Joined: Apr 2010
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    Location: pomfret ct

    kenrahe Sunseeker

    top cylinder still not running with the new plugs havent got the carb off yet to clean an check reed valves
     
  13. capt littlelegs
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    capt littlelegs New Member

    If you've eliminated plugs and leads then as said it could be ignition coils etc. however a heathly spark is a good indication that all's well there. It could also be the top crank oil seal/bearing or a broken reed valve. You may be able to use something like a a colour tune to check the spark under compression as further verification. Unlikely to be a single carb if running on one cylinder.
     
  14. kenrahe
    Joined: Apr 2010
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    Location: pomfret ct

    kenrahe Sunseeker

    is single carb. how do i do a colour tune.an whats the easyest way to check the resistance on the coils
     
    Last edited: Apr 20, 2010

  15. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    have you checked the pick-up coils under the flywheel yet? You need to take the flywheel off for that. Do not confuse the charging coils for the ignition pickup coils.;)

    "whats the easyest way to check the resistance on the coils" For the DIY guy it is best to use a normal multi meter set to resistance (ohms)and measure across the coils windings.
    However, if you have a healthy spark on that motor, I would again advise you to look at the reed valve. As said before, your Merc has a single carburetor and if one cylinder fires up good, the other should as well and that eliminate a possible fuel problem.

    If this was in my shop, I would first check the reed valve - easy to take of carb and inspect it. Since you have already changed the spark plugs I would then home in on the coils - change coils around and see if the other cylinder goes on the blink and the top one firing up. If this is the case, easy then, replace the coil.

    If no change, check the aforementioned pick-up coils under the flywheel. Hope this helps.
     
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