Mercury 40hp 4cyl oil injection

Discussion in 'Outboards' started by rosbullterrier, Oct 12, 2015.

  1. rosbullterrier
    Joined: Feb 2005
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    Location: Cornwall, UK

    rosbullterrier Junior Member

    Last year I purchased this outboard, aprox 1992, because I really fancied this four cylinder smallish outboard. I've only just mounted it ready to try.
    Anyhow after repairing the oil injection bottle and reading up which pump nozzle is in or out, I'm having cold feet over using the oil injection at all - instead of premixing the fuel just to be be safe.
    My thinking for using the injection is to use less oil at idle and prevent too much smoking. (no I have not started it yet!)

    My question - is the amount of oil pumped a variable ratio with the revs.
    I appreciate less comes through with lower revs but does the ratio decrease below 50:1 and then increase up the range.
    If not I might as well play safe and mix it all at 50:1 previously in the tank.
     
  2. whitepointer23

    whitepointer23 Previous Member

    It is variable but it doesn't matter. Just use premix. Modern oils are very good anyway. I get a puff of smoke from my old johnson when it starts and then it is clear. Doesn't oil up with new oils either.
     
  3. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    that certainly go to about 100:1 or more at idle
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Could be as little as 200:1 at idle with some engines, but be 50:1 at full revs, pre-mix is always calculated for maximum rpm. If the thing works, why change ?
     
  5. whitepointer23

    whitepointer23 Previous Member

    As long as he makes sure the warning buzzer is working before using it.
     
  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Yes, I would do the same. Lots of Johnson VRO engines have died from a faulty oil pump because the alarm buzzer only sounds when the oil tank is nearly empty, not if the oil flow is interrupted for other reasons.
     
  7. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    that was fixed when they went to the 4 wire pump which was also a replacement part
    Hard to measure oil flow at 100:1 and idling
     
  8. rosbullterrier
    Joined: Feb 2005
    Posts: 83
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    Location: Cornwall, UK

    rosbullterrier Junior Member

    Thank you gentlemen.
    I read the Mercury warning buzzer only operates for low oil not it's output.

    There is a section in the manual which actually states the outflow expected at certain revs but I didn't know whether it would have been less than the 50:1 at low revs.
    Maybe I'm being a bit paranoid but the oil injection tank was not connected when I got it and the seller (who was not the user) said he would premix instead of depending on the oil pump.
    The oil pump drive gear on the end of the crank I read is plastic and can deteriorate from overheating - if it's available
    To get parts for Mercury's from the US costs a fortune in shipping and being obsolete they're difficult to find as well!

    What would be your opinion to use full synthetic oil?
     
  9. whitepointer23

    whitepointer23 Previous Member

    If it is disconnected do not use it. Synthetic oil is good. Premix and you know the engine is getting lubricated.
     

  10. rosbullterrier
    Joined: Feb 2005
    Posts: 83
    Likes: 2, Points: 8, Legacy Rep: 21
    Location: Cornwall, UK

    rosbullterrier Junior Member

    Thank you sir. I shall take your advice and start it tomorrow . . .
     
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