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Thread: Glowing manifolds

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    Bodger Turbosport Subscriber

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    Glowing manifolds

    I have an issue where my manifolds are glowing red. This is just letting the car idle and then free revving it to about 3,000 rpm for about 20 seconds or so once the engine is up to temp. Also when I switch it off I get a backfire through the exhaust.
    Engine is a 711m crossflow 1700 all steel stage 3 244 camshaft twin 40 Weberís all new and just built compression ratio about 10.5:1
    The ignition timing is set at 14deg at idle and about 34deg at full advance so should be Ok. I had a wide-band Lambda checking the AFR and it was fluctuating between 14 and 15: 1 at idle blip the throttle and it goes rich briefly but settles back to around 13 or 14. So not particularly rich and certainly not lean. At this sort of rpm and throttle opening I guess it will not be progressing to mains yet so shouldnít be an issue with mains chokes etc . Compression test resulted in about 180psi on each give or take a couple of psi (was done cold)
    The engine sounds fine throttle response free revving is Ok so Iím pretty stumped.
    Any ideas would be great.
    I did post this problem a year or so ago and thought I managed to resolve it with help here as I had the wrong Carbs but the project was put on hold and back on it now with New correct carbs and jetting that should be ok as a starting point.
    Chris
    Last edited by chris52; 14-01-2018 at 12:25.

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    Re: Glowing manifolds

    Glowing exhaust header usually means running lean.

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    Re: Glowing manifolds

    hold any engine with a tubular manifold at highish rpm for any length of time with no airflow and it will glow so you may noty qctuall have an issue

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    Re: Glowing manifolds

    Surprised you get a decent idle with AFR as lean as that. Anything the engine is doing whilst in a garage and not under any load will always be suspect / not truthful.

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    Re: Glowing manifolds

    Thanks Guys what AFR should the idle be at? On all the EFI engines with Lambda fitted it’s usually around 14.7:1 controlled by the ecu/Lambda
    Chris

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    Re: Glowing manifolds

    Thanks Guys what AFR should the idle be at? On all the EFI engines with Lambda fitted itís usually around 14.7:1 controlled by the ecu/Lambda
    Chris

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    Re: Glowing manifolds

    Carbs can't meter fuel accurately enough to match EFI - they are making ten's of micro adjustments to fuel and ignition timing per second. Carb idle hot would usually be sub 13:1 and cold anything down to 10:1 and could vary based on flywheel weight / ignition timing as it could be misfiring (6 stroking) and the flywheel / timing will keep it spinning over.

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    Re: Glowing manifolds

    Glowing exhaust manifold is usually rich mixture and/or late ignition timing.
    What idle jet are you using?

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    Re: Glowing manifolds

    Thanks for the help a simple 1/4 turn out of all the idle screws sorted the problem. No glowing manifolds and no popping through the exhaust on shut off. Will get it to the RR to be properly set up once I get it on the road and a bit of running in of the engine done. AFR on Idle now is fluctuating between 12 and 13:1.
    Cheers Chris

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    Re: Glowing manifolds

    Generally this is caused by retarded ignition timing so try advancing it a few degrees to see if it helps, otherwise your cam timing could be retarded (inlet mixture entering exhaust on overlap)

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    Re: Glowing manifolds

    .

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    Re: Glowing manifolds

    Quote Originally Posted by Miniliteman View Post
    Glowing exhaust manifold is usually rich mixture and/or late ignition timing.
    What idle jet are you using?
    Spot on, to late (slow burning in the case of rich mixture) mixture. Add more advance by using a vacuum canister (or program more advance for the younger generation). Check mixture but with the extra advance it should be better.

    As Graham also says, it will always glow after some time but it it's cherry red very fast, above.

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