Float Height for Carburettors due to Ethanol in Fuel

Discussion in 'Mech Tech' started by Patrick Nguyen, Aug 4, 2020.

  1. When I got my IDF's from Eurocarb I dismantled them and cleaned and set the floats to 10mm. When they arrived they were well over 10mm and not the same either carb, so I just assumed they had not been set.

    However after watching a few youtube videos, Weber are recommending setting the float height at 14mm due to the new fuel mixtures.

    So with this in mind should we use the same logic to our Solexes, Dells and basically any other carb.

    Yes I understand it may affect jetting a little, but technically no because the fuel level would be close to correct as the Ethanol fuel would have been sitting at a incorrect higher level.

    Any thoughts
     
  2. Zed

    Zed Gradually getting grumpier

    10 to 14mm is a lot.
    What would be handy is measurements down to the fuel in a complete carb. That could be checked by removing a main stack and dipping down the hole. I think I saw a post from Modoc on Samba with that suggestion and possibly a measurement for DRLA40's IIRC.
     
    Deefer66 and Patrick Nguyen like this.
  3. If it's down to density..

    I'd have thought the weight of the float would be better to adjust as the level is quite important as to which jets are operating i thought...

    and is it really that different?

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    Patrick Nguyen likes this.
  4. Zed

    Zed Gradually getting grumpier

    I assume the float adjusting is intended to result in the same fuel level for a denser fuel? That why I thought decreasing the float height by 40% was OTT, 10% ethonal can't be that dense.
     
  5. Zed

    Zed Gradually getting grumpier

    Petroleum sg = O.739
    Ethanol sg = 0.79
    5% ethanol + 95% petroleum
    (0.05x0.79)+(0.95x0.739) = sg = 0.741
    I won't be adjusting my float height.
     
    mgbman, mcswiggs, andyv and 3 others like this.
  6. docjohn

    docjohn Supporter

    Yes, I agree. I've got some data on specific gravity of petrol as a function of octane rating (RON) from the late 1950s through to the late 1970s and some modern race fuels. There's not a discernable difference between summer and winter even though the blending changes to increase volatility in the winter. There's a slight increase with increasing RON from 0.72-0.74(ish) at 90 RON to 0.74-0.76 at 100 RON. Modern race fuels over 110 RPN are lower density, 0.71-0.74 so clearly a completely different type of blend.
    I've not found any data for modern E5/E10 fuels but I'm sure you are in the right ballpark with 0.74.
    The density also drops with temperature, about 4% from 0C to 50C.
    Since it is the level of the fuel in the chamber that is important, the float gap is a bit of an indirect way of doing it given the number of variables.
     
  7. Love it when the maths comes out. Weber say the ethanol increases the oxygenation in the fuel which makes he floats not as effective.

    So I'll leave my floats at 10mm unless I start running into drivability issues.
     
    Zed likes this.
  8. The coefficient of expansion of Ethanol is more than petrol, somert to chew over.
     
  9. Zed

    Zed Gradually getting grumpier

    Do you have a link?
     
  10. ... and there's some say increasing jet sizes to account for ethanol burning behaviour.. best get mine running properly before I worry about that

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    paulcalf likes this.
  11. mikedjames

    mikedjames Supporter

    At the moment, with the E5 to E10 mixes, they are so close to older fuel mixes its not worth changing.

    A lot of this is in the mind of some Americans. Some Americans are descended from people who travelled 5000 miles or more to avoid changing their ways.
    Adding ethanol to petrol is a heresy, and an abomination in their minds.
    The fact is nobody could tell you exactly what was in petrol before ethanol became one component, apart from the guys who controlled the mix that went in the tanker for delivery that day,.
     
    docjohn and Valveandy like this.

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