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Rough Idle - Honda 50 hp - Carburated Version

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  • Rough Idle - Honda 50 hp - Carburated Version

    My Honda 50 hp runs rough at idle in gear.
    It operates fine at all higher power settings.
    It is the carburated version (not fuel injected).
    The engine is about 5 years old.
    Any suggestions would be appreciated.

    I was told that Honda set these engines VERY lean to meet EPA and California emissions laws, and that the solution is to remove a "welch" style plug on each carburator and set the mixture richer.

  • #2
    Do not remove the welch plug. Your motor will be even worse. Plus, Honda does not sell new ones.

    Check the spark plugs and first make sure that they are all burning the same.

    It is possible the the idle mixture is out on one of the carbs...however, generally once they are set, they do not have to be reset.

    Some of the things that will cause a rough idle.

    Too high oil level.
    Thermostat stuck open (motor not coming to temperature)
    One or more carburator running too lean or too rich.
    Idle passage in one or more carburators clogged.
    Carburators not vacuum balanced.
    Valves clearances out of adjustment.
    Bad compression

    Generally, you can pull the spark plug wires one at a time while the motor is idling (used insulated pliers).. The motor should slow down or even die as you pull each plug wire off the spark plugs. If there is no change in the motor speed, then that is the cylinder that has the problem. It could be the spark plug, cylinder itself, or something in the carburator.



    • #3
      Uncle Mkie

      The Honda Shop Manual (Publication # 66zv300) on page 3-8 refers to adjusting the "Pilot Screws".

      Tighten all of them until closed, then back them out 2 & 1/8 turns, then turn carb #3 pilot screw 1/8 turn at a time to obtain highest idle speed.
      Then perform the same adjustment on Carbs 1 and 2.

      Are "pilot screws" changing the idle mixture? I'm not familiar with the term "Pilot Screws".



      • #4
        Honda calls them pilot screws. They are also know as idle mixture screws.

        Yes, they control the air and fuel mixture at idle.



        • #5
          Uncle Mike

          The "pilot screws" have a 'wing' or arm on the side of the screw heads.
          These 'wings' prevent continuous rotation of the screws becuase they are stopped by a ridge on the carb body.
          These screws are turned out as far as these stops will allow so I can't make the mixture any richer. The body of the carb looks like plastic so I didn't want to twist these screws very hard.

          Any suggestions would be appreciated.