My Merc 25 2 stroke:

Discussion in 'Outboard Maintenance' started by richwalker71, Jan 8, 2012.

  1. richwalker71

    richwalker71 Well-Known Member

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    Will not wind up to max RPM with out pulling the primer knob out. With it out she runs wide open. What gives?
     
  2. Brett

    Brett > PRO STAFF <

    Not getting enough fuel.
    Possible fouled carb or air leak.
     

  3. richwalker71

    richwalker71 Well-Known Member

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    So what is it bypassing by opening the primer?
    Doesn't this eliminate an air leak in the fuel line/bulb/tank, etc.?
     
  4. Gramps

    Gramps Living &amp; Dying in 3/4 Time

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    If you take off the cowling and the black plastic piece covering the carb throat you'll see what the primer knob does. Pulling the knob out closes a butterfly like flap, limiting air into the carb/motor.
     
  5. Brett

    Brett > PRO STAFF <

    Informative read...better than me trying to type... ;)

    http://www.smallenginesrepairs.com/small-engine-choke.html
     
  6. richwalker71

    richwalker71 Well-Known Member

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    Thanks guys. That link should help alot!
     
  7. Creek Runner

    Creek Runner Well-Known Member

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    Is this the same motor you had the same problem (Not turning all the way up) a few weeks back? I thought you put a Control Module on it and fixed it?
     
  8. richwalker71

    richwalker71 Well-Known Member

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    You are correct! Had a mechanic diagnose/install that fairly pricey little beauty.
    Ran much better but never felt "right". This last trip it started this new problem.
     
  9. levip

    levip I Love microskiff.com!

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    its the carb
    pulling out the choke (or primer knob as it called on this one) closes the intake tract and pulls more fuel through the venturies in the carb and thats why it runs better tear the carb down, dip it and reassemble with a new carb kit

    dont run it like this anymore untill you rebuild the carb or youll burn up a cylinder or a piston because as it is now its running lean
     
  10. richwalker71

    richwalker71 Well-Known Member

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    Did just that levi. Sort of. Didn't do a complete rebuild, but found a couple of screws on the side plate of the fuel pump loose and the gasket on the bottom of the bowl was iffy. Tightened screws and replaced gasket.

    Did a quick test run today and it ran great.