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Thread: 1987 Supersprint carburetor adjustment

  1. #1
    Join Date
    Jan 2020
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    135

    Default 1987 Supersprint carburetor adjustment

    I have a quick question before I have a shop work on calibrating and cleaning my Weber DCOE 40s.

    Is it normal to have the Crossflow engine hesitate and spit when throttling up from idle? Mine is fine when idling and when above 3000 RPM, but in between I get a lot of popping, spitting and hesitating. Some of it is undoubtedly caused by the aggressive cam, but my hope is that the carbs can be set up so it is smoother on the road and in traffic.

    Thanks/Anker
    1987 Caterham 1700 Supersprint
    2002 Porsche Boxster
    2004 Porsche Boxster S
    1941 Dodge Luxury Liner
    2009 Mercedes CLK 350 Cabriolet
    2017 Chevrolet Volt

  2. #2
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    Jan 2006
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    I've had three cars with DCOEs, including a Crossflow similar to yours (1700cc, Kent 234 cam). None of them had the issue you describe. The closest was a built Alfa that used new casting DCOEs with progression holes that didn't work well with the engine, and would go through a rich/lean/rich cycle when cruising around 3000rpm.

    Have you already verified the basic settings are correct? Float height, various jets and emulsion tubes? Have you synchronized the carbs? Checked for air leaks when they attach to the manifold? Confirmed timing is correct? Occam's Razor doesn't seem to apply to DCOEs, so even if you find several of these things out of whack, you could still need a rebuild.

    -John
    '95 Westfield SEiW w/2.0L Duratec
    '68 Lotus Elan FHC
    '91 Miata w/Flyin Miata suspension & brakes
    '95 Porsche 993 C2
    '86 Porsche 944 turbo (neglected project car)
    Throttle Steer

  3. #3
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    Jan 2020
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    I have checked and adjusted float heights, adjusted the idle screws as specified, and synchronized the carbs. The first thing I did was to replace the gaskets between the carbs and the intake manifold with the Swedish ones (can't remember their name). There definitely aren't any air leaks. I also replaced the distributor and coil (Lucas electronic ignition) with a new distributor and coil from Burton Power with an Aldon Ignitor. The ignition timing is spot on. In short, I have done all that I feel competent to do.

    It is better than when I purchased the car, but not to my satisfaction.

    The information I needed is that this is not normal. It will be going to a specialist shop that knows how to set up Webers next Thursday.

    I appreciate the reply!

    Thanks/Anker
    1987 Caterham 1700 Supersprint
    2002 Porsche Boxster
    2004 Porsche Boxster S
    1941 Dodge Luxury Liner
    2009 Mercedes CLK 350 Cabriolet
    2017 Chevrolet Volt

  4. #4
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    Someone here may know the correct jetting for the Supersprint spec engine. If not, I'd try BlatChat for that info. Someone in your car's past may have tried to "improve" things by playing around with chokes, various jets, or emulsion tubes, and screwed things up. I've even heard from someone who discovered a random PO had changed the emulsion tube in just one carb, creating a mismatch. Always good to know if your starting point is correct.

    -John
    '95 Westfield SEiW w/2.0L Duratec
    '68 Lotus Elan FHC
    '91 Miata w/Flyin Miata suspension & brakes
    '95 Porsche 993 C2
    '86 Porsche 944 turbo (neglected project car)
    Throttle Steer

  5. #5
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    Jan 2006
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    Seattle-ish
    Posts
    1,448

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    See this thread on BlatChat. It has the settings for a stock Supersprint (post #2) and feedback from folks on issues they've chased and what jetting worked best.

    -John
    '95 Westfield SEiW w/2.0L Duratec
    '68 Lotus Elan FHC
    '91 Miata w/Flyin Miata suspension & brakes
    '95 Porsche 993 C2
    '86 Porsche 944 turbo (neglected project car)
    Throttle Steer

  6. #6
    Join Date
    Oct 2019
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    SE NC
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    Is it hesitating on WOT between idle and 3k, or on gentle acceleration, or both?
    Henry
    1965 Seven S2
    1969 Elan S4

  7. #7
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    Oct 2006
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    Cincinnati
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    As another point of reference, I can say my 1700cc SuperSprint X-flow Caterham engine never did that. Lots of cool popping on deceleration. Maybe BBall will offer his thoughts, he has chased many X-flow engine demons.

    And, on a related mater, both BBall and I had huge problems with our carbs due to worn engine mounts. The engine moved (a lot) as a result of the worn mounts, the air filters poking out of the bonnet were then forced against the edge of the bonnet, causing a vacuum leak and resulting in poor running. This only occurred on left hand turns. The X-flow mounts are a high wear item and should be swapped out every 5K miles or so, FWIW.
    Last edited by Kitcat; 07-30-2020 at 06:35 AM.
    Kitcat:AKA, Sir Spinsalot
    '97 Caterham Super Sprint, 1700 Crossflow-sold
    '09 Birkin S3, Duratec-sold
    '03 Caterham Zetec track car
    '19 Honda Type R, sold
    '19 Miata Clubsport

  8. #8
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    Jan 2020
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    Quote Originally Posted by SENC View Post
    Is it hesitating on WOT between idle and 3k, or on gentle acceleration, or both?
    If I stomp on the throttle it does better, so the acceleration pumps seem to be doing their job.

    I will pull the emulsion tubes and compare them with the recommended ones.

    Thanks for all the suggestions/Anker
    1987 Caterham 1700 Supersprint
    2002 Porsche Boxster
    2004 Porsche Boxster S
    1941 Dodge Luxury Liner
    2009 Mercedes CLK 350 Cabriolet
    2017 Chevrolet Volt

  9. #9
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    Oct 2019
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    Given that, my first look would be at the idle jets. I'd pull them and blow them out first. What # idle jet are they? And what size choke do you have? I'd also inspect to see how the progression holes look as the butterflies open.
    Henry
    1965 Seven S2
    1969 Elan S4

  10. #10
    Join Date
    Sep 2005
    Location
    St. Louis, MO
    Posts
    461

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    Do you know what cam you have? I have the Kent 244. Believe I have the “normal” setup for a 244. I can pull what I can this weekend and let you know.

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