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Thread: Question on fuel consumption of my BN6

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    Question on fuel consumption of my BN6

    Hi gents,


    depending on driving style and weight of the co-pilot my BN6 uses 18-20 liter fuel per 100 km. In my perception that is pretty much. I refurbished the carbs last year without any noticable improvement. Also checked the emission, but nothing remarkable on that.

    Is that much consmption expcted? If not, does anyone have an idea how to proceed to improve the situation?

    Volker

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    Jedi Knight bighealeysource's Avatar
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    Re: Question on fuel consumption of my BN6

    Hey Volker,
    Gonna have to convert that over to gallons for us Yanks ! I had a 58 BN6 that did average around 25 miles per gallon when driving around a constant 55-60 mph. Would think usual would be in low 20's. One thing you might check is if you are running too rich which would impact the mpg. On the other hand though, if it's running good, don't touch it as I like to practice the "if it a'int broke, don't fix it" philosophy !!!
    Regards
    Mike
    Mike Lewis, 1956 Austin Healey 100M - Registry Confirmed

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    Re: Question on fuel consumption of my BN6

    Hi Volker
    Sounds about right given the differences between the Liter and The Imperial gallons
    Odometer accuracies, tire sizes and driving styles.
    Last edited by Keoke; 08-14-2014 at 05:30 PM. Reason: Expand the variables
    1966 Daimler V8 Saloon; Safely Fast, Built to Last & and; Smooth as Glass.
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    Re: Question on fuel consumption of my BN6

    Mike,

    I checked if I am running too rich by measuring the emission of the car. According to my garage I am running more less than too rich. I share your opinon that you should not touch a running system. My car is indeed running fine.

    Did I understand it right, that in your opinion 18-20 liters per 100 km (for a German guy) is not neccessarily unusual? When driving on a high way constantly about 60/65 mph at 3000 rpm the car consumes a little bit less (15-18 per 100 km).

    Regards,

    Volker

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    Re: Question on fuel consumption of my BN6

    Assuming 4 liters per gallon and .6 miles per kilometer, 20 liters/100 km comes out to be 5 gals per 60 miles, which is about 12 miles/gal. Most healeys get around 20 mpg I think. I'd say you're either running really rich or leaking gas.
    Keith
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    Re: Question on fuel consumption of my BN6

    Keith,


    I checked if I am running too rich by measuring the "CO-Value" by putting a sensor into my exhaust pipe. It seems to be good according to my garage. What is a "good" CO-value from your point of view? By the way: In my understanding the "CO-value" is the portion of the carbon monoxide in my exhaust.


    What do you mean by "leaking gas"?


    Volker

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    Re: Question on fuel consumption of my BN6

    Volker,
    I have no idea what a good value for CO is, but maybe someone else on the forum will know and chime in. I tune my carbs using the "lift the piston a fraction and listen to the rpms" method. And by "leaking gas" I mean quite literally gas dripping from somewhere in the system; float bowl overflowing, gas leaking from the bottom of the jets, loose gas line connections, etc.

    Hope this helps. I do think that 12 mpg is low for highway driving. It might get that low for very spirited around town driving.
    Keith
    '59 Bugeye (recently restored)
    '62 BT7 (recently restored)
    '65 Sprite (restored 30 yrs ago)

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    Re: Question on fuel consumption of my BN6

    I'm running a Denis Welch DW8 cam, two HD8 SU's, California oxygenated fuel, headers and a lead foot in my 3-liter BN4. Last I measured, I was getting 17 mpg (14 liters/100 km).

    By "leaking gas", I think he means liquid fuel is leaking on the ground and not being used by the engine.
    John, BN4

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    Re: Question on fuel consumption of my BN6

    Try pulling the plugs after a 5+ miles and check the color. You are looking for a nice tan color. If rich it will be black.

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    Re: Question on fuel consumption of my BN6

    Your fuel consumption equates to about 15 miles per imperial gallon (real gallons). That is high consumption for a BN6 which should be getting about 20mpg at least.

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    Re: Question on fuel consumption of my BN6

    My BN6 runs about 11-14 liters/100 km. depending on the driving style. Check if the correct carb needles are fitted.

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    Darth Vader AUSMHLY's Avatar
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    Re: Question on fuel consumption of my BN6

    I also had bad mileage. Highway MPG was where it should be. Around town/highway combination was terrible. Seem it was the distributor. Had it rebuilt and mileage increased to what others were getting.
    1964 BJ8 phase II

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    Re: Question on fuel consumption of my BN6

    I get 23-25 mpg in my 100 Lemans with the larger SU's and a DW "Fast Rallye" cam.

    As I recall my ex-wife's stock 3000 gave about 21-23. I sure miss that car.

    Best--Michael Oritt
    1954 Austin-Healey 100 Le Mans
    1959 Elva MK IV Sports Racer
    1961 Ginetta G4

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    Re: Question on fuel consumption of my BN6

    John, what are the "correct" carbs needles? I refurbished the cabs two years ago.

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    Re: Question on fuel consumption of my BN6

    "AUSMHLY", can you explain me the dependecy between the distributor and fuel consumption, please. I cannot imagine any :-(

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    Re: Question on fuel consumption of my BN6

    .. unwanted resistance and bad voltage ...
    The least I can do is keep my CarClean.com
    Jaguar X type 2.5, 2003 Carnival Red Metallic
    Austin Healey HBJ8L/40871,MkIII ph2 April 1967 Original MGBeige, now BRGreen

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    Re: Question on fuel consumption of my BN6

    "BigGreen", can unwanted electric resistance and bad voltage really influence fuel consumption? Indeed that could be a good starting point for further analysis. I would really appreciate if you could detail on this. Volker

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    Re: Question on fuel consumption of my BN6

    Incomplete combustion or incorrect timing can have an effect on fuel mileage. If the distributor is not advancing properly that can effect it.

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    Re: Question on fuel consumption of my BN6

    The standard needles for a stock BN6 are CV. (Those identification marks are on the upper portion of the needle). Rich needles are marked RD and lean needles SQ.

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    Re: Question on fuel consumption of my BN6

    Quote Originally Posted by BN6_2197 View Post
    "AUSMHLY", can you explain me the dependecy between the distributor and fuel consumption, please. I cannot imagine any :-(
    Sorry, I can't. Maybe someone here can explain it to you.
    1964 BJ8 phase II

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