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Thread: Cabrio carb

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  1. #11 Re: Cabrio carb 
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    Hi,
    The carburetor has been blown through with compressed air as mentioned earlier in this thread a total of three times to no avail. Every fuel way, every jet, main and secondary blown through with compressed air.
    I don't have the facilities to drill out plugs accurately not a job I would under take.
    Thank you both.
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  2. #12 Re: Cabrio carb 
    frequent forum contributor Club Member greyV8pete's Avatar
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    The fact that the mixture screw doesn't do anything is suspicious. Which suggests too rich from other jets or no idle fuel supply. So I would want to be sure that there isnt anything in the fuel gallery supplying that. Silicone sealant is a no no with fuel as it swells up and blocks things. Also is the float level correct? Another thought is the automatic choke working correctly. Is it pulling off smoothly or sticking closed / fully rich? Peter.
    Last edited by greyV8pete; 15-03-2020 at 11:15 PM. Reason: Open to closed correction
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  3. #13 Re: Cabrio carb 
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    Hi Peter,
    I don't know what else to say. I think there is a restriction some where in the carburetor, all that has been suggested has been carried out.
    I have read on this forum similar problems with this carburetor which was only cured by replacement.
    I think I may be following this route.
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  4. #14 Re: Cabrio carb 
    frequent forum contributor Club Member greyV8pete's Avatar
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    You wrote in your first post
    “Lastly having carried out the work the mixture screw does nothing”
    Do you mean that the mixture screw did nothing after the strip down or despite the strip down and clean?


    Has the hunting gradually become worse or did it start suddenly? Have you done any other engine or distributor work recently? Has the vacuum advance unit in the distributor failed. The diaphragms can fail after long service giving a weak mixture which the mixture screw cant cope with? Put a vacuum pump directly on the units vac connection and see if moves the contact breaker plate and if it holds its position.


    Is there any chance that the primary and secondary progression jets and emulsion tubes have been swapped around somehow in error?


    Another thought is to check that the secondary throttle flap is closed at tickover and maladjustment or failure of the operating diaphragm unit isn’t letting it stay open? Also check the secondary throttle plate is opening at the correct time relative to the primary. The workshop manual should give you all the settings.


    As a final thought have a look at the gaskets for the power valve and accelerator pump valve. I seem to remember that on my Sierra (different carb) the sort of triangular shaped ones can be fitted either way up. Could this have happened and is maybe blocking a fuel hole?


    Also check the accelerator pump bleed back / non return valve isnt stuck open. Also check that you can see a jet of fuel squirt into the carb barrel when the throttle is opened quickly.


    Keep chipping away. Its got to be something simple that is causing the problem! Peter.
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  5. #15 Re: Cabrio carb 
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    Hi Peter,
    I'll answer your questions as layed out...
    1). Mixture screw does nothing.
    2). Hunting became worse.
    3). No vacuum advance ( e c u)
    4). Diaphragms replaced.
    5). No breaker plate. ( e c u)
    6). Primary&secondary emulsion tubes original and in original places.
    7). Secondary throttle flap closed at tick over.
    8). Power valve & accelerator valve gaskets replaced.
    I have this after noon bought a new after market fuel pump. The pressure of the Ford pump may be suspect, only way for me to check this is with a new fuel pump. The pressure should be about 2 psi according to Webcon. Webcon suggested the carburetor may not be getting enough fuel could be starvation.
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  6. #16 Re: Cabrio carb 
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    If acceleration is Ok and its running well at steady throttle I can't see fuel starvation as being the cause of rough idle. It just doesn't add up to me.
    Has the car been idle over the winter or in regular use, and has the problem just materialised or got worse over time?
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  7. #17 Re: Cabrio carb 
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    Just read on one of the Ford forums that there is a potential cause of poor idle from a small rubber hose behind the exhaust manifold . Seems they crack over time /heat. Replacements have metal shield to prevent this taking place. Maybe worth checking.
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  8. #18 Re: Cabrio carb 
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    Hi,
    It doesn't add up to me neither.
    There isn't a rubber hose behind the exhaust manifold. Having spoken to Webcon it's their opinion that fuel starvation my be the cause of hunting.
    So I bought an after market pump to see or at least eliminate the Ford pump from the equation.
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  9. #19 Re: Cabrio carb 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Aha! Not familiar with that engine so didn't realise you had an ECU. So does it have an idle control valve? If yes then go straight there. Whip it off and clean it out. The ones fitted to the Sierra injection models were notorious for giving poor and fluctuating idle. My friend who had one kept a spare cleaned one in the boot. Swapped it at the first signs of a problem. Then cleaned the other one and popped it back in the boot! On second thoughts maybe only a full injection set up has one?

    Agree with dogoncrazy that low fuel supply is unlikely. Checking that hose he mentions sounds like a good lead. Peter.
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  10. #20 Re: Cabrio carb 
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    Hi,
    There is no rubber hose.
    Until I fit and tryout the after market pump I won't know for sure if it is the Ford pump which maybe at fault. A low fuel supply is a contributory factor to hunting, poor idling Webcon said but we will have to wait and see.
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