Latest News: Forums Technical 4 stroke outboard question

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  • #4202
    mhardman
    Member

    I have heard that, when done with the outboard, you should close the fuel valve and let the engine run out of fuel. Is this necessary on a 4 stroke? I mean the fuel is pure fuel without oil mixed in, so I’m thinking it shouldn’t gum up the carb when it evaporates.

    Thanks for indulging me with another question that’s only tangentially relevant to Wayfarers!

    #9462
    tempest51
    Member

    Fuel stays “fresh” for only about 3 months, no problem in a car usually. What you should always do is empty any fuel in the carb, easy to do and takes a couple of seconds. Turning off the valve is also a good idea, and in theory the carb should be empty. I know to my own cost that fuel will clog up your carb, so why risk it? I tend to empty any old fuel into my car and fill up the can with fresh fuel. There are fuel stabilizers that you can buy, that hold fuel for longer periods…good for lawn mowers over winter.

    #9463
    triton
    Participant

    @mhardman wrote:

    I mean the fuel is pure fuel without oil mixed in, so I’m thinking it shouldn’t gum up the carb when it evaporates.

    Petrol is derived from crude oil, the oil is still there, just more refined.
    When petrol evaporates, it leaves behind a sticky deposit known as lacquer and varnish. In time, this can become quite hard and clogs up the small passages in the carburettor………which is bad news.

    #9465
    mhardman
    Member

    Thanks for the replies, will start running the carb dry. Though the engine is so efficient, it takes ages!

    #9466
    tempest51
    Member

    There you go mhardman good luck, by the way what part of Scotland are you from? 😀

    #9467
    krgough
    Participant

    This is one of those questions that you can answer in two ways ie. what should you do and what do I actually do…

    I would say that running the carb dry every time I turn the engine on is not practical and in fact I never do it. What if you’re driving up to a beach? Do you loiter for a couple of minutes with enough water to run the engine to dry out the carb and then when it cuts out paddle for the beach – Probably not – You probably run in cut the engine and drift up onto the beach with the carb still full.

    In theory I suppose you should flush the engine in fresh water every time you use it and I suppose you could run the carb dry when doing that. But I wonder how many of us don’t bother. I certainly don’t do it every time. Actually on mine when I tried to close the fuel valve and run it dry it seems to suck fuel from somewhere and I get a little fuel leak, never quite worked out where it come from – it never leaks in any other condition – on it’s side in the boot of my car it is fine.

    My little 2-stroke Suzuki sits all winter with the same fuel in the tank/carb and it starts pretty much first time. when I first got the engine from my dad it had very old fuel (10yrs??) and would not start. Fresh fuel – 1 pull and off it went. Engine is about 20yrs old. The main issue (with this particular engine) is not carb gunking but overheating due to the cooling channels blocking with salt/sand. I spoke to a Suzuki mechanic about that and his opinion was that flushing on small engines was good to do but does not really stop cooling channel blocking. He said the only way to stop it for sure was to use the engine regularly – most of us don’t so they crust up. Only cure is to remove the head once in a while (every couple of years) and scrape it out – easy enough on a 2 stroke. On mine you need 2 gaskets – cylinder head and exhaust gasket. If they come off is reasonable condition I re-use then with a bit of gasket compound. The only thing to be careful of is not stripping the threads when you re-assemble.

    regards

    Keith

    #9469
    triton
    Participant

    Just to clarify, you do not need to run the carburettor dry after every use if this is not practical.
    I would do it before any long period of storage.

    Unless the outboard is being used regularly in sea water, then I would flush out with clean water after use.
    Nothing worse than impeller blades sticking to the pump casing due to salt water drying out.
    They are then shed as you start to turn the engine next time out…….we learn by our mistakes.

    However, characteristics of engines do vary so so just do what preventative maintenance is necessary to avoid problems.

    #9470
    tempest51
    Member

    mhardman,

    Some of the advice written here seems maverick to say the least, why not consult the manual that came with the engine or indeed seek more sensible advice?

    #9471
    krgough
    Participant

    Oh dear – It’s a shame when it descends to insults.

    #9473
    mhardman
    Member

    Well I have the manual but I was looking for real-world experience of people who use the boat, and the engine, like I do. Which I got. Thanks everyone.

    #9474
    Swiebertje
    Participant
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