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Thread: No change to idle when ignition lead disconnected from #4

  1. #1
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    No change to idle when ignition lead disconnected from #4

    I was getting my timing checked out as I've put a H&H distributor in with their coil pack.


    Just wanted to make sure I done the job right and it was doing what it was meant to - at idle it is 10 deg and at ~3k it is about 30 deg so reckon that's within the range as specified in the haynes manual


    Anyway while I was there the machine we were using had the option to cut the feed to eat ignition lead. Thought it would be worth a try.


    The results were
    ignition lead 1 disconnected - 17.5% drop
    ignition lead 2 disconnected - 13.2% drop
    ignition lead 3 disconnected - 22.9% drop
    ignition lead 4 disconnected - 3.4% drop


    I am a bit confused as to why there is so little difference when No 4 is disconnected.


    I have ruled out the coil as I believe they work in pairs. IE - if 2 and 4 (or 1 and 3) both had low values then it would be a bad one - is that right?


    I have ordered new plugs, ignition leads, dizzy cap and rotor arm and will re-try soon and swap a good result with the bad one and see if it follows or not

    Compression test shows two at 170 and two at 180 so all fairly close

    Car appears to be driving and idling fine and made 143 bhp at the fly recently

    Is there anything else I can check?

  2. #2
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    Re: No change to idle when ignition lead disconnected from #4

    Twin carbs?

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    Re: No change to idle when ignition lead disconnected from #4

    Yeah twin 45s

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    Re: No change to idle when ignition lead disconnected from #4

    Probably carbs not completely synchronised and/or bent throttle shaft / throttles.
    At idle the opening of the 4 throttles is not the same hence difference in rpm drop.
    You can check it by measuring vacuum on all cylinders.
    At higher rpm the difference in throttle opening is not important.

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    Re: No change to idle when ignition lead disconnected from #4

    Sounds like it's either a plug, lead or the dizzy cap to me.

  6. #6
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    Re: No change to idle when ignition lead disconnected from #4

    1 to 4 - roughly 5,6,5 and 7 from the air intake gauge thing used to balance them.

    Cleaned everything up properly and tried again with just the timing light connected to see rpm drop.

    All seemed good this time except I couldn't get a reading on number 1 but that's not one I was bothered about. Could also hear it struggle

    Hope to get back on the machine to double check.

    Hopefully that's it solved and the car has had a good check over again.

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