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  1. #1
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    4th cylinder not running well

    i have a problem bringing my fulvia berlina S2, 1300, into "good running order":

    car purchased from a collector. hence it was not used for a long period.

    car starts on the button, no smoke, no unusual noises, but idling is not stable, even carbs are well synchronized.

    investigations turned out that the 4th cylinder is not running well (exhaust manifold colder than the other 3 cylinders)
    the 4th cylinder also doesnt react on the mixture adjusting screw of the rear chamber of the solex carbs.

    i have meanwhile changed plugs, ignition leads, breaker-contact. i have played with igniton timing. i have made a compression test where all cylinders are equal. i have checked valve clearances, as the above mentioned problem sounded to me like the 4th cylinder has no clearance. also here everything fine.

    both carbs have the same fuel level. fuel is fresh, fuel is clean, all jets have been cleaned. swapping jets from front to rear carb to front carb and vice-versa, did not move the problem. (mechancial) fuel pump is also new.

    i´m now running out of ideas.

  2. #2
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    Re: 4th cylinder not running well

    Have you actually checked that there is spark at that cylinder - you can either attach timing light to that cylinder or simply hold the lead just off the engine and have someone else turn the car over. It can only be no fuel, or no spark, or no compression and you seem to have eliminated lack of compression. I would also recheck fuel delivery perhaps by visually checking that fuel is pumped into the barrel when the linkage is operated past halfway open. You can also use some easy start before you attempt to start the engine, just spray into no.4 carb generously - if it goes normally you know it is a fuel problem, however I always start diagnosis by checking ignition first.

  3. #3
    Experienced Lancista AJMA11's Avatar
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    Re: 4th cylinder not running well

    Quote Originally Posted by alfas View Post
    ...i have meanwhile changed plugs, ignition leads, breaker-contact. i have played with igniton timing. ...
    I would say the same as alfavirusnz...

    about ignition, you did investigate everything and change quite everything BUT the distributor cap !
    it may well be defective only for the fourth cilinder,
    check the cap for :
    cracks (might be invisible), damage, corrosion, burnt or dirty cord hole, burnt or moving electrode terminal, etc...

  4. #4
    Experienced Lancista Akonaut's Avatar
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    Re: 4th cylinder not running well

    Just an idea.

    Isn´t the vacuum for the brake servo taken from the inlet of cylinder #4? Sounds a little bit as if #4 suffers from false air. Unplug the vacuum hose from the cylinder head stub and close the stub properly. If the engine then works, check the booster.

    It has also been reported that the rubber connection flange between carbs and manifold ages and gets cracks leading to false air. Not necessarily on #4 only
    Hubert
    Flaminia GT 3C, Flaminia Convertibile 3C, Flaminia Coupé-project-, Flavia Convertibile 1.8, Fulvia Sport 1.3S, A112 Abarth 70HP, Mercedes Benz Unimog U406

  5. #5
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    Re: 4th cylinder not running well

    @akonaut:

    good advice...even i have no "hissing" noise which usually indicates a fautly booster, i have the feeling that the booster is not working well.

    for the others:
    off course i have checked already the sparks: there are healthy sparks on all 4 cylinders.

    i meanwhile also found out that spraying some WD40 (or similar) on the rubber carb-flanges, idle slightly increases., more effect with rear carb, than front...so new rubbers now in order.
    Last edited by alfas; 21st July 2019 at 04:10 AM.

  6. #6
    Legendary Lancista lancialulu's Avatar
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    Re: 4th cylinder not running well

    Is the 4th plug "wet" after running a bit showing no firing but petrol?

    Can you put a "colour tune" into the spark plug hole to see what combustion you are getting?

    Does the 4th cylinder work at higher revs or when the engine is warm???

  7. #7
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    Re: 4th cylinder not running well

    during dirving 4th clynder was working.

    i put now some sealant on top of the carb-rubber flanges...and here we go...idle is stable.

  8. #8
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    Re: 4th cylinder not running well

    Quote Originally Posted by alfas View Post
    during dirving 4th clynder was working.

    i put now some sealant on top of the carb-rubber flanges...and here we go...idle is stable.
    Hubert
    Flaminia GT 3C, Flaminia Convertibile 3C, Flaminia Coupé-project-, Flavia Convertibile 1.8, Fulvia Sport 1.3S, A112 Abarth 70HP, Mercedes Benz Unimog U406

  9. #9
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    Re: 4th cylinder not running well

    today the rubber-flanges arrived....changed them, incl. new gaskets...and problem came back again ...even worse than with the old rubbersand sealant

    when i spray some WD40 near the flange of the 4th, espeically in the area of the mixture screw, idle increases.

  10. #10
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    Re: 4th cylinder not running well

    Have you sprayed wd40 around the butterfly spindles?

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