4hp 4 stroke Yam

Discussion in 'Outboards' started by RedBaronj, Nov 12, 2011.

  1. RedBaronj
    Joined: Nov 2011
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: London

    RedBaronj New Member

    Yamaha 4hp . Engine has only about 15 hrs running time. Runs only with the
    choke pulled out. Stripped and cleaned carb with carb cleaner & compressed
    air, replaced fuel filter, symptom still persists.
    Would be greatfull for any ideas.
  2. Rangerspeedboat
    Joined: Apr 2009
    Posts: 120
    Likes: 3, Points: 0, Legacy Rep: 17
    Location: Texas

    Rangerspeedboat Senior Member

    If it only runs with the choke out then its running lean, my guess would be an air leak after the carburetor. Does the carb have a gasket on it?
  3. Frosty

    Frosty Previous Member

    This is main jet. The choke restricts the air pulling fuel through the half dirty jet.

    Water in these tiny carbs is the biggest problem and leaves white calcium that will not blow out.
  4. RedBaronj
    Joined: Nov 2011
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: London

    RedBaronj New Member

    Tried that before with jet cleaners.
    Thanks anyway.


  5. kenJ
    Joined: Jul 2005
    Posts: 349
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Williamsburg, VA

    kenJ Senior Member

    I agree on the plugged main jet. Quite often it takes poking with a wire followed by the carb cleaner and air to unplug them. I've seen one or two so bad that the jet was completed blocked, looked like solid metal. I wasn't till I started poking did the jet become visible.
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 494, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Ditto the jets, but also the bleed and other passages inside the carb need to be chased with a "sized" wire orifice ream. You can run carb cleaner through it all day, but if it's the over the counter stuff, it's weak and not very effective. The good stuff is 10 times as strong and the carb needs to soak in it for hours.

    Since your engine has such low hours on it, it's very likely you have an obstruction in one or more of the passages. Depending on the year of your engine, you may have deteriorated fuel lines and rubber parts, that are depositing little bits of hard nuggets into the fuel stream. These can drive you nuts as they can be so small that you can't see them, but 2 of them can partly block a vent or other passage, making you run super lean.

    Buy a set of orifice reams and carefully go through the carb with the appropriate sizes, after a long soak in cleaner. Rinse then blow out. It would be wise to examine the inside of the fuel lines for crumbly surfaces, which is a big tell.

  7. bruceb
    Joined: Nov 2008
    Posts: 1,259
    Likes: 47, Points: 48, Legacy Rep: 214
    Location: atlanta,ga

    bruceb Senior Member

    all of the above- and?

    Did it ever run correctly? Also, does it run any better if you keep pumping the fuel line bulb? B
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.