Merc 6HP 4 Stroke - only runs at speed with the choke out ??

Discussion in 'Outboard Maintenance' started by RustyReel3755, Aug 20, 2009.

  1. RustyReel3755

    RustyReel3755 I Love microskiff.com!

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    I have a 6hp 2004 Merc 4 Stroke that doesn't want to run much faster than idle.  I did a search of the site and most guys seem to have the opposite problem, that is engine won't idle without the choke out, but run fine at faster speeds.

    Mine starts up fine and idles fine, once it is a little warm, but if I give it the gas it will bog down, coughing and sputtering and will even shut itself off unless I back it down to idle.  IF I pull the choke all the way out, and leave it out,  it gets up and goes fine.

    I drained the bowl using the drain screw, shot a little carb cleaner in there to flush it out but it doesn't help.  At first I thought it may be the fuel line (I don't like the fit of the connection from the fuel line at the motor) but getting fuel from the tank shouldn't be a problem if it runs fine with the choke out....should it??

    My next step is to run some sea foam thru it. 

    Do you think this thing needs a carb rebuild or ???? what.  Any help will be appreciated.  Thanks!

    RustyReel
     
  2. Brett

    Brett > PRO STAFF <

    I think your high speed jet is partially blocked.
    By closing the choke you increase the vacuum in the throat
    and force a fuel flow into the intake manifold.
    I'd do a complete rebuild of the carb.
    I've got the Nissan version of the same engine.
    Same problem solved by cleaning the entire fuel system
    and then doing a complete rebuild of the carb.
    The carb kit cost less than 40 dollars.
    Very simple carb to work on, only hard part is the primary bolt closest to the flywheel.
    Almost no room to work a wrench.
     

  3. noeettica

    noeettica Well-Known Member

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    Post some photos of the motor and carb ...

    there should be a main jet in the bottom of the carb and possibly an emulsion tube above that
    get them out and cleaned and you will be well on your way to getting this fixed
     
  4. RustyReel3755

    RustyReel3755 I Love microskiff.com!

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    OK, here are some pics, hopefully.  I removed the black screw at the bottom of the carb bowl and flushed it out a couple of times with carb cleaner.  The gas that came out of it when I first opened it looked clean. 

    Haven't had a chance to mess with it any more but hope to do so over the weekend.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  5. Brett

    Brett > PRO STAFF <

    You've got 2 open hose connections on top of the carb.
    Are there hoses or caps that cover those 2 barbs?
    If not, that may be your problem, an air leak.
     
  6. TomFL

    TomFL Well-Known Member

    Brett, if he's got that much air coming in past the butterfly I think it'd idle at 3,000 RPMs

    -T
     
  7. Brett

    Brett > PRO STAFF <

    No, I gave that some thought before posting,
    Had an old Carter YF that actually idled better with a vacuum line disconnected,
    and would stall out when you increased the throttle.
    I miss those old engines. Now you can't work on a car
    without a serial cable, 200 bucks worth of software and a laptop computer.

                                              :D
     
  8. RustyReel3755

    RustyReel3755 I Love microskiff.com!

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    Those open hose connections had me wondering as well.  In case you have not figured it out, I'm not much of a mechanic.

    Searched Merc parts sites for pics of the carb.  They all had the same drawing with not much detail, those ports were not shown.

    Did an Ebay search and found two listing for the same year and size motor with pictured detailed enough to see the carb.  Both of those motors also had these ports uncovered.  So I'm guessing that is the factory set-up?

    They must do something, however, as this AM when I had the motor at idle I covered them with my fingers and the motor started to sputter.

    I don't know.  Still gonna give the seafoam a try when I can get around to it.  Some guys claim it works wonders....others not so much.

    Thanks guys.
     
  9. noeettica

    noeettica Well-Known Member

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    Had to jump through some hoops to post this but here U go ...

    [​IMG]

    Dave
     
  10. Brett

    Brett > PRO STAFF <

    that's one way to get a screenshot Dave... ;D

    Here's a piece of software that lets you capture an image direct from your desktop...

    http://download.cnet.com/Gadwin-PrintScreen/3000-2094_4-10123018.html
     
  11. noeettica

    noeettica Well-Known Member

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    Thanks I will try that ... I took a photo of the desktop screen... Loaded it into the notebook then put it on photobucket then refreshed photobucket on this machine and pasted the Link
    :D 

    Oh Btw Cheap OLD Nikon 775 These early point and shoots work great ! 775 , 880 , 885 & 5000 Got a bunch of 'Em LOL
     
  12. RustyReel3755

    RustyReel3755 I Love microskiff.com!

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    Thanks NoeTtica, that is the one I found. Doesn't show the vacuum ports on the top of the carb and what, if anything, gets attached to them. Tks, and sorry for the jumpin' thru the hoop.
     
  13. RustyReel3755

    RustyReel3755 I Love microskiff.com!

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    Thanks guys.  Sea Foam did the trick.  Roarin' to go now!!  Actually, I'm still puttering along since it is only a 6 horse, but better than before.
     
  14. TomFL

    TomFL Well-Known Member

    Awesome!

    -T