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Thread: My Kilo Motor

  1. #51
    Team Member 850cc racer's Avatar
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    well the boat will be flying so not sure what fuel ill run
    not sure on that one?

    what do you think is good?

    850

  2. #52
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    As with any OMC race motor they would say 4%, 25:1 and the jetting would be to suit that.
    Adding oil leans out the mix and vice versus
    They say 25:1 for added safety so I guess for a kilo run you could use less maybe 40:1 and therefore lean out the jetting to suit.
    Do you have the original jet sizes for the Mod 50?
    You might want to have an EGT proble/gauge to test that though.
    http://www.vpracing.com.au/
    http://www.racefuels.com.au/
    http://www.etracingfuels.com
    www.mjfmotorsport.com.au

  3. #53
    Team Member 850cc racer's Avatar
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    well thats some interesting info. i will take that onboard...how would adding oil lean it out?.. 25:1/30:1 is where i have always ran my single throat 75 and havent had any probs.

  4. #54
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    If the fuel jets are passing a lot of oil then there not passing as much fuel.
    The oil isn't really part of the mix so less fuel is the result of more oil
    Just something to be aware of when altering your oil ratio

  5. #55
    Team Member 850cc racer's Avatar
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    if you mix the oil and fuel as you need it and mix it well the jets are passing the "mix" not just oil or fuel..?

  6. #56
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    Yes but the the mixture now contains more oil.
    The jets meter liquid subject to the air going past.
    If the mix has more oil in it what comes out of the jet is more oil and less fuel per unit volume therfore fuel air mix is leaner.

    Same amount of air has gone into the engine, same volume of liquid.( your mix)
    its just that liquid is now made up of more oil and hence less fuel.
    NB Ensure you dont get fuel with ethanol in it that will also lean it out.

  7. #57
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    ahhh im with ya bigger jets then

  8. #58
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    I think you'll find that increasing the amount of oil in the fuel changes the viscosity & the thicker mix finds it more difficult to flow through the jets at the same rate.

    Very few 2 strokes are ever short of fuel in the combustion chamber, they're usually short of the air to burn it!

  9. #59
    Sam Cullis Mark75H's Avatar
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    Can you provide evidence? I use the same jetting for 32:1 and 24:1

    it just isn't so
    Since 1925, about 150 different racing outboards have been made.


  10. #60
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    Sam fill a coke bottle with oil & then fill one with straight gasoline, then time how long it takes to empty the bottles, I know this is a bit extreme but it's just to prove a point.

    The difference between 40 :1 & 25:1 is only 15 ccs per litre, not a whole heap of difference, might well get away with the same jets, but try that with an early motor that runs 10: 1 & compare that to 25 : 1 & there's 60 ccs per litre difference, that might well need a jet change.

    It's easy to get fuel into a motor just the cost of some jets, getting more air in there to burn it, costs a lot more cash.

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