99 25hp Merc Primer knob

Discussion in 'Outboard Maintenance' started by richwalker71, May 13, 2010.

  1. richwalker71

    richwalker71 Well-Known Member

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    This is the first motor I have owned with this knob. Read the Merc manual as far as using it (starting procedure). Is it basically, pull to choke and a fast idle when you turn it open (clockwise)? I assume this is to help the engine warm up, right? Do i need to turn it back down before opening up the throttle?
    Thanks,
    TRW
     
  2. mark_gardner

    mark_gardner I Love microskiff.com!

    not really, all that knob does is bump the idle up a hair. it's possible that motor could use an idle adjustment anyways
     

  3. love2flyfish

    love2flyfish Well-Known Member

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    Like SB said, its just adjusts the throttle a hair. I would say if it sounds like its idling high, turn it back down. Also be aware that the choke on that motor is a pump to choke, if you look closer, all the choke knob does is push down a built in primer pump.

    Good luck with your motor!
     
  4. richwalker71

    richwalker71 Well-Known Member

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    Pretty much what I thought. Thanks guys.
    TRW
     
  5. Un-shore

    Un-shore Well-Known Member

    Wait. comeback!

    I'm not near my motor to check but I think it also advances the timing. I don't know if it would damage the motor running it like that but you never know
     
  6. mark_gardner

    mark_gardner I Love microskiff.com!

    that advanced timing rod is a joke :eek:, i've run the piss out of these motors without one ( timing advance linkage) if your motor sounds like its wanting to die out while idleing on the water hose just bump the adjustment screw under the cowling and you'll be good to go :cool:
     
  7. richwalker71

    richwalker71 Well-Known Member

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    The only problem I've had is the motor will "bog down" and die every once in a while when I open the throttle quickly. Seem like it floods out. It seems like this happens less frequently if the knob is "open" part way. Other than that it runs like a top.
    Someone else suggested this could be a timing issue. I think it's fuel/carb related. Any suggestions?

    TRW
     
  8. noeettica

    noeettica Well-Known Member

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    WHILE WERE AT it how in the %^&* do you set the timing and why do these motors buck just above idle ... Dave
     
  9. mark_gardner

    mark_gardner I Love microskiff.com!

    never messed with the timing on mine as i never needed to but that timing advance linkage has a lot of slop to it so i cant really say whether they're really all that effective or not :-/ mine will bog a little sometimes also just feed it slow and steady till she perks up then lite your candles ;) :cool:
     
  10. Weedy

    Weedy Well-Known Member

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    I lost that timming advance linkage on mine (05 motor), she still will run without it!!!
     
  11. richwalker71

    richwalker71 Well-Known Member

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    Think I figured out the bogging problem: My exhaust dips below the water coming out of the hole. The extra back pressure is causing the problem. If I trim the motor up a bit, she spins right up. :)

    PS- Found a new school of fish during testing this afternoon :cool:
     
  12. WannabeDeepSea

    WannabeDeepSea Well-Known Member

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    Not that it is...but it could also be running a little rich. If you have fixed your issues ignore, if it continues to be a problem then:

    There is a fuel/ air mixture screw located on the carb in the front of the motor. It is the one located above the primer knob by maybe 2" and has it's own access hole through the air shield. Anyway, if you are idling rough or bogging, it might need to have an adjustment(please only adjust if necessary- a motor that runs rich is better than one that runs lean when it comes to the life of the motor).

    Adjustment:
    After proper idle speed adjustment. Start the engine, put it in gear at idle. Adjust the mixture screw counterclockwise until it misfires(due to being too rich). Then count the turns while adjusting it clockwise till it once again misfires(this time too lean). Divide the turns you counted by 2 and turn the screw counterclockwise to find the happy medium. Too rich is better than too lean.

    I am not an outboard mechanic and do not claim to be, but having the same issue with a 25hp carb I installed on my 20hp, this cleared it up. The information was a summary of what was written in a manual I used to tune the new carb- worked great.
     
  13. richwalker71

    richwalker71 Well-Known Member

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    Thanks. Plan on fishing pretty hard this weekend so if the problem persists I may give that a shot.
    TRW
     
  14. mark_gardner

    mark_gardner I Love microskiff.com!

    agreed, thats good info.... thanks :cool:
     
  15. WannabeDeepSea

    WannabeDeepSea Well-Known Member

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    One quick note I forgot, be sure to run the motor a little to warm it up to full operating temp before adjusting, otherwise it will not be an accurate adjustment.
     
  16. Un-shore

    Un-shore Well-Known Member

    A little late to the dance, but it should normally start with the exhauast lowered so it is indicating a small adjustment is needed.
     
  17. richwalker71

    richwalker71 Well-Known Member

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    Re: 99 25hp Merc Primer knob UPDATE

    Went ahead and leaned her out a tiny bit. Results were no more bogging in the hole shot, smoother idle, and I swear it starts even easier than before. Thanks for the suggestion.
     
  18. mark_gardner

    mark_gardner I Love microskiff.com!

    so how abouts did you get to running lean? did you just mix the oil lean or an adjustment on the carb ? the leaner you run it the hotter she's gonna run just dont want to scorch a piston :( but if you can find her sweet spot you should be good to go ;)
     
  19. cutrunner

    cutrunner Cert. Yamaha technician

    lean is mean. give it all the timing you can :) if everythings under control, your going to slow. Mario Andretti
     
  20. richwalker71

    richwalker71 Well-Known Member

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    I did the adjustment suggested by Wannabe'. Wound up with the adjustment screw about an 1/8 of a turn closer to the lean side. Still running standard mix on the oil/gas.

    I'm no mechanic so now you guys got me worried. :-/
    Am I in danger of damaging the motor?