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Hairpin bends in a carb car

Discussion in '308/328' started by francisn, Aug 13, 2020.

  1. francisn

    francisn Formula 3

    Apr 18, 2004
    1,820
    Berks, UK
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    francis newman
    Talking to friend who has just done an Alpine pass tour in his 599, and who commented on some of the difficulties on the hairpins even in that car, reminded me of my own experiences in the Alps and the Picos D'Europa in my carbureted non power steering 308GT4.

    If you haven't driven a carbureted car then you won't know that in hard cornering when the throttle is dropped there entails a lack of fuel to the carbs and the engine stalls.

    My solution is to drop the clutch on exit of corner, two dabs on the pedal bipping the throttle to keep the engine revving then drop the clutch. Not too good for clutch wear but is that the only way to do it?
     
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  3. miked

    miked Formula Junior

    Feb 7, 2001
    665
    Cincinnati, Ohio
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    Mike Dawson
    There is a well known fault of 308 carb cars of the engine stumbling in corners. Many people have solved that characteristic by installing baffles in the float bowls to prevent the fuel from sloshing away from the jets. Haven't heard any discussion on the subject or a source for the baffles in many years.
     
  4. Albert-LP

    Albert-LP F1 Veteran
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    Sep 1, 2010
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    May I ask you if you had that problem only with sharp airpins at high altitudes in the Alps or also (e.g.) on a sharp U turn at sea level?

    If it only happens in the Alps, in my opinion the problem is another

    ciao
     
  5. Ferraridoc

    Ferraridoc F1 Veteran

    Jun 20, 2012
    9,531
    Gold Coast, Aust.
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    Patrick
    No Albert, it happens at sea level too. I have experience with side draught webers, and always understood that it was flooding causing the problem - fuel sloshing in the float bowls allowed the floats to drop, letting too much fuel in. I run a fuel pressure regulator in my race car, which mitigates the problem, but I'm not familiar with how down draught webers work.
     
  6. Jasonious

    Jasonious Rookie

    May 13, 2018
    42
    PNW
    I would suspect improper float level adjustment or sticking needle valve. The other possibility is a weak fuel pump or clogged filer/gunk in the tank. Carbs generally don't starve for fuel if all components in the fuel system are setup correctly and are working properly.
     
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  8. Albert-LP

    Albert-LP F1 Veteran
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    Sep 1, 2010
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    Side draught Weber DCOE can give some small problem like that, but not so big as described by Francisn.

    Downdraft Weber DCNF doesn't suffer of that problem in such a way.

    Ciao
     
  9. francisn

    francisn Formula 3

    Apr 18, 2004
    1,820
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    francis newman
    I think stumbling as a better word than stalling for what I experience. I will talk to my carb experts to see what they think.
     
  10. jmaienza

    jmaienza Formula Junior
    Silver Subscribed

    Jan 8, 2009
    501
    Massachusetts
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    Joe
    I have read that due to the orientation of the float bowl reservoir on these particular carburetors (aligned sideways as opposed to front to back) the fuel sloshes around and creates fuel starvation as the car leans into the curve.

    I think it is more prominent when you take an aggressive, left hand turn and the car leans to the left. At that point, the gas flows to the left, raises the float and pushes the needle valve up, thereby slowing or stopping fuel flow into the bowl. I think that is how it was explained to me. I have only experienced it once when I was taking a very aggressive series of "S" turns in a parking lot and throwing the car sideways back and forth. Definitely fuel starvation.

    When the carburetors are aligned front to back (as they were designed to be mounted that way) the shift in fuel level would be minimal because the front or back would not rise or fall as much as a sideways lean into a turn.
     
  11. francisn

    francisn Formula 3

    Apr 18, 2004
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    francis newman
    That makes some sense as my problem is mainly on left hand bends
     
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  13. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,435
    Along the Verde , AZ
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    I used to notice the problem.

    But, when I had the motor upgraded to 3.6L last year, the carbs were rebuilt.

    Not just a gasket change and float setting, but completely rebuilt, throttle shaft bearings, emulsion tube well reaming, everything, made as new.

    I have not noticed the problem since. Maybe i just haven't thrown the car around sharp corners hard enuf, but i think i have.

    I do know, when the car was just few year old, 37 yeasr ago, I didn't seem to have the problem, but it got worse with age over the years, before the upgrade.

    Doug
     
  14. Portofino

    Portofino Karting

    Sep 17, 2011
    228
    Yorkshire UK / Switzerland/ Cote d Azur
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    Portofino
    Never Noticed it .
    I did 500 km of alpine stages last summer in a classic car rally.Many many hairpins .
    Also I left it in Switzerland for 4 months so did loadsa hairpins uneventfully.
    208 with smaller 34 carbs .
     
  15. Albert-LP

    Albert-LP F1 Veteran
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    Sep 1, 2010
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    As said, only bad working carbs give that problem: it's not allowed (of course) that a Ferrari engine stalls on an hairpin and this his should be obvious to everyone.
    I'm sorry but the problem is aging of the carbs (seals, floats, dirty and so on) and or the necessity of carbs tuning and or fixing the fuel pump. The problem is not given by the lack of fuel but it's caused by a too rich air/fuel mixture ratio at sea level that at high altitudes becomes even richer due to air lower density. When you approach an hairpin you release the gas pedal for long time with the engine high revving so you have high vacuum conditions in the intake manifolds: when you firmly push down the gas at the mid of the hairpin, the booster jets flood the intake manifold with a big quantity of fuel to give you the big power you are asking for. This makes your A/F mixture ratio so rich that it doesn't even burn anymore: you have to wait that the engine spits out all that excess of fuel so that the spark plugs can fire up the mixture again. Please check your spark plugs: they will be black.

    Tune or rebuild your carbs.

    Ciao
     
  16. JuLiTrO

    JuLiTrO Formula Junior

    Nov 2, 2017
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    Julio Saiz
    Perhaps you are not entering the corner fast enough
    Keep those RPM high!
     
  17. francisn

    francisn Formula 3

    Apr 18, 2004
    1,820
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    Thanks Albert, although I did also notice the problem on a low altitude hill climb I did here in England a few years ago.
    I don't think the fuel pump is the problem as I had a new one 4 years ago.
    It's not really a major problem for me as it is very seldom a drive hairpins but I do like to have things right.
    I will talk to my experts at QV here in UK and see what they think and if I have enough budget maybe have a rebuild over the winter.
     
  18. francisn

    francisn Formula 3

    Apr 18, 2004
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    Beliee you me I was entering the corners as fast as was possible but having to brake hard so not that easy to keep the revs up
     
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  19. Albert-LP

    Albert-LP F1 Veteran
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    Sep 1, 2010
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    Francis, I didn't want to force you to do anything: I just wanted to tell you that it's not normal to have such a big problem. I own the same car and never experienced that problem on hairpins or U turns. There must be some problem inside the carbs: they are not perfect like a digital fuel injection, but they must work well everywhere

    Ciao
     

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