505 carby transplant operation
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  1. #1
    Member
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    505 carby transplant operation

    While their is talk of carbies in the air, currently I have a 505 '83 GR which has had a Weber carby converted it seems from auto choke to manual choke at sometime. The Weber has been assessed by the mechanic as being well worn and is resulting in excessive fuel consumption (about 5km/L).
    Also it is making a cold start difficult. Used to be 4 or 5 turns,now about 8 or 9.
    The Weber manual choke does indeed operate the single butterfly valve from an open to closed position but this does not seem to have any effect on the mixture as would be expected.

    My other 505 '82 GR has had its Solex auto choke carby replaced by a second hand unit from Pugwreck. The mechanic who replaced the unit did a fine job but announced at the same time that this car has a corrupted engine (another long winded story).

    But what I wish to do is change the carbies myself. Are there any known difficulties in this?
    For instance manifold differences or gasket variations.

    Also can someone explain to me why the Weber has only one butterfly valve present. Thought this was contributing to my starting problems, but experimenting with a rag stuffed in the open inlet made starting impossible!
    __________________________________________

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    Rgds,
    Peter.

  2. #2
    Fellow Frogger!
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    Hi, quite a few of the webers fitted here in Canberra had the second choke flap removed. I think it was as they were mostly set up a bit rich (jets) and leaving out the choke flap made them less likely to flood when using the choke. I doubt it was having any effect on your starting.

    Cheers

    jim

  3. #3
    Fellow Frogger! AlsPug504's Avatar
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    [QUOTE]<strong>PUG 504 505: manual choke at sometime. The Weber has been assessed by the mechanic as being well worn</strong>

    In what area?

    <strong> and is resulting in excessive fuel consumption (about 5km/L). Also it is making a cold start difficult. Used to be 4 or 5 turns,now about 8 or 9.

    The Weber manual choke does indeed operate the single butterfly valve from an open to closed position but this does not seem to have any effect on the mixture as would be expected.Also can someone explain to me why the Weber has only one butterfly valve present.</strong>

    Depends, but the top butterfly, called the strangler flap is attached to a device called a choke pull off.

    When you pull on the choke the flap closes denying air from entering. So the engine vacuum pulls fuel only ie richen mixture! When the vacuum increases a small piston is drawn against spring pressure to open the choke flap. Return your mixture to normal.

    When you popped that rag in there as a replace ment for the flap you flood the engine with fuel. That is why it was hard to start. The butterfly you moved quite possiblily was the throttle. No enrichment in mixture would occur if it were left shut. If you pump the accelerater, that will pump more fuel into the engine.

    <strong>Thought this was contributing to my starting problems, but experimenting with a rag stuffed in the open inlet made starting impossible!</strong>

    Your hard starting condition will be because the engine does not get suffient fuel vapour.

    Or your flooding it with vapour.

    If your fuel usage is high. Get the mechanic to check you part throttle and Idle mixture ratios with an O2 sensor, and a gas anlyser with HC & CO. Or just use colortune. The mechanic should be able to correct your mixtures.

    Also get them to check the needle and seat does not leak! Replace (new) any powervalves (They leak lots!). Adjust float level. Check your mixture screws are not scored.

    Als wink

  4. #4
    Guru davemcbean's Avatar
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    From my experience, on two stage (progressive) carburetors, a choke flap is usually only necessary on the first stage throat. This opinion is confirmed by the fact that many types of carburetors now only come with a choke flap on the first stage. Basically the second stage throat is always closed at idle anyway, so the choke flap is redundant.

    I've found that with choke flaps on both stages of a carby, that some cars will not take full throttle while the choke is on, whilst with a choke flap only on the first stage, things are fine.

    Dave

    <small>[ 25 July 2003, 06:38 PM: Message edited by: davemcbean ]</small>
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  5. #5
    Budding Architect ???? pugrambo's Avatar
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    dave
    you are right there
    with most of the webers i have seen over the years the progressive ones only have the choke flap on the primary throat (ie inline engines) it's only the simultaneous opening carbs that have the choke flaps on both throats (ie webers used on V6 engines )
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  6. #6
    Gone Fishin' Ray Bell's Avatar
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    Ah for the simplicity and easy servicing of an SU...

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