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Thread: 3.5 V8 County SU Carburettors stuck open

  1. 3rd January 2016, 02:24 PM #1
    Carslil Jim's Avatar
    Carslil Jim
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    3.5 V8 County SU Carburettors stuck open

    Hi,
    I have oiled every moving part and the carbs mechanism wont return to the "stops". I was driving yesterday and just before I got home it caught but then released, but now the carbs are stuck about 1/3rd open.

    Any ideas??
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  2. 3rd January 2016, 05:44 PM #2
    dromader driver
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    what type and how much damper oil do they have??
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  3. 3rd January 2016, 07:31 PM #3
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    BigJon
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    Pull the tops off and clean the pistons with carby cleaner. They probably have a gunk build up on them jamming them in the bores.
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  4. 3rd January 2016, 09:05 PM #4
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    lebanon
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    Check your throttle cable, sometimes it does this.

    You can oil it by dismantling it from the engine side.
    Hold it to the vertical while spraying WD40 or silicon spray between the cable and its jacket.
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  5. 4th January 2016, 06:00 AM #5
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    Carslil Jim
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    What a good question! There was NO damper oil, and I have now added engine oil which is what I usually use. I know lighter oil ought to be used but I have not had any problems (perhaps until now), using the 20W-50.

    That had not fixed the problem as of last night, so i will now pull the tops off and clean the pistons.

    The cable seems free enough but I will oil it next if we still have the problem

    Thanks to you both for suggestions. I will report as we go.

    Jim
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  6. 4th January 2016, 06:50 AM #6
    bsperka
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    Damper oil is just that ; determines how quickly goes up or down. Engine oil is fine to use if you want slower response. It's not a race car. Dust or dirt on the outside of the piston is most likely the problem. Needles could be bent but this is usually when they have been roughly handled.
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  7. 4th January 2016, 08:57 AM #7
    dromader driver
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    sewing machine oil worked well in my mini SU's. think it is about 10 wt
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  8. 4th January 2016, 05:00 PM #8
    bsperka
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    If its an SU then the cable has no impact on the piston being stuck. Only impacts the piston if there is vacuum; that is when the engine is running.
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  9. 4th January 2016, 05:58 PM #9
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    lebanon
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    I have been using ATF oil for the SU with good throtle response.

    As for the cable if it is not perfectly free it might keep the throtle mechanism, i.e. butterfly open.
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  10. 5th January 2016, 07:33 AM #10
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    Last night I removed the pistons and I could see the butterflys were closed....but the mechanism is about 1/8 inch off stops, the accelerator pedal is sloppy and I can see slack in the cable at the carby end. Cleaned the pistons which were easy to remove (ie not stuck). Blowed if I can see what is stopping the mechanism from sitting on the stops.

    I will assemble later today and start her up and see if it idles normal or runs fast.

    Its a wonderful life kneeling on a padded board across the front of the engine and bending over this problem. I have released the bonnet stay and pulled the bonnet vertical to give me a little more headroom so I can see this thing clearly. I managed to spill engine oil all over the place while flailing around with this problem. Competence is coming into question!
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