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  1. #1

    Default Honda 5hp 4 stroke outboard problems

    Any suggestions for the resolution of my problems with the above gratefully received.
    The motor is less than 2 years old, but had not been used for perhaps 1 year when I bought it. The fuel has been replaced, the fuel line has been flushed, and the fuel tank has been rinsed with fresh fuel. The motor has been serviced.
    It is reluctant to start. Once started it will not idle, and stalls after perhaps 15 seconds.
    The fault is intermittent: on one occasion I started the motor perfectly three times, each time allowing it to cool down. Then two days later, the fault reappeared.
    The fault may possibly be due to a modification made by the previous owner. He attached a metal tube about an inch long to the idle port, to which he attached a three inch long plastic tube. I don't know why he did this. I have removed the plastic tube, but the metal fixing might be difficult to remove without causing damage.
    So the questions are:-
    1) Pardon my ignorance, but what does the idle port actually do?
    2) Could the described fault be due to this modification?
    3) I suspect that the fault appears when the weather is cold. Would this modification particularly effect performance in cold weather?
    4) Any other suggestions?

  2. #2
    Join Date
    Jul 2007

    Default Re: Honda 5hp 4 stroke outboard problems

    OK, as an ex owner of this worthy-but-underwhelming engine, I can assure you that:

    1/ Cold starting is not nice. They start, and are most recalcitrant for a minute or two.

    2/ When you shut the engine down, run it with the fuel tap closed, until the engine dies of fuel starvation, or you run the risk of old fuel gumming up the idle jet.

    3/ The engine, while idling, is fed fuel via a small petrol jet. When you open the throttle, a larger main jet supplies fuel in addition to the smaller one. The smaller one is the size of a needle-hole, so gums up easily, affecting the idling if so afflicted.

    so: Use fresh fuel, run the carb dry, and accept this modern lean burn engine won't run well for a minute or three from cold! [img]/forums/images/graemlins/smirk.gif[/img]
    Scand 32 Atlantic

  3. #3

    Default Re: Honda 5hp 4 stroke outboard problems

    Do you mean the exhaust idle port?

    If so the modification was probably to get rid of the exhaust gasses when the engine was used in a well.

    As I understand it the port is simply to let the exhaust out of the engine when the engine is running slowly because it wouldn't have enough "oomph" to get out through the normal port. (The pressure of water would stop it...a bit like the school-boy trick of bunging a spud up a car exhaust)

    Of course I may be completely wrong.......

  4. #4
    Join Date
    Jul 2007

    Default Re: Honda 5hp 4 stroke outboard problems

    No, the exhaust port is just where the exhaust gasses exit the engine, and unless blocked, wouldn't affect starting.

    Try cleaning the carb jets, otherwise, assuming the idle speed and mixture are fine, accept it's a dog to start, which is why everybody prefers the older engines...
    Scand 32 Atlantic

  5. #5

    Default Re: Honda 5hp 4 stroke outboard problems

    Many thanks for your responses, folks. I think I see some light at the end of the tunnel. I can see the point of the tube. The motor does indeed sit in a well. The tube ensures that exhaust gases are discharged outside the well: without it the exhaust gases will be discharged into the well, from where air is drawn into the motor, and Without fresh air, the motor will stall. This may also explain the intermittent nature of the fault: if there is a wind blowing perhaps the wind may flush the exhaust gases out of the well.
    Now the manual warns against having the idle port (as it describes it) too near the waterline, as this will obstruct the flow, leading to poor starting and stalling. The addition of the tube to the idle port will presumably have the same effect, so I was wondering if there might be other solutions to this problem, which must be common where outboards are mounted in wells. Perhaps the motor could be raised, say, an inch so that there is a reasonable air gap around it, as it is, currently, quite a tight fit. Any suggestions?

  6. #6
    Join Date
    Sep 2005

    Default Re: Honda 5hp 4 stroke outboard problems

    I would be carefull. For some unknown reason my eboat has been retrofitted with an outboard well. I ran my long leg 5hp honda in this when racing as I wasn't allowed it on its normal bracket and its too heavy to heave about when 2 handed and trying to sail.

    The motor did not like being run at low revs and would stall. The exhaust gassess washed over the cockpit sill into the cabin and set off the carbon monoxide alarm. If running in a well make sure it is properly ventilated and there is a route for the exhaust gasses to escape to, especially if it is a later addition to the boat. My well now serves as a massive cockpit drain and beer cooling system.

  7. #7

    Default Re: Honda 5hp 4 stroke outboard problems

    Personally, I would put the plastic tube on again (long enough to lead the gasses to the outside world). Try it like that and see what happens.
    Whilst I don't know your engine this is a common DIY mod which normally casues no problem. When I fitted a two foot tube to my engine (Mariner) it stopped the Carbon Monoxide alarm problem overnight.

    If that doesn't work, then try cleaning the carb as already suggested.

  8. #8
    Join Date
    Oct 2003

    Default Re: Honda 5hp 4 stroke outboard problems

    I think the idle port modification is OK - another reason for the idle port is to avoid sucking water back up the exhaust as the engine cools down, or if it 'bounces' backwards on starting or stopping.

    One thing to check is that the exhaust gasses aren't bubbling back up into the well from the main exhaust.

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