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Re: Dieseling

Subject: Re: Dieseling
From: (James Fischer)
Date: Thu, 28 Dec 1995 08:01:39 -0500
    Craig Wiper asked:

>I just decided to throw my Weber 32/36 downdraft back on the B. My SU's
>don't like the cold weather much. My question is: Is there an easy way to
>prevent dieseling when cutting the ignition with these carburettors? With
>the SU's many vaccuum ports I am able to prevent the dieseling by having the
>anti-runon valve attached. But with the Weber, I only have one vaccuum port,
>which attaches to the vaccuum advance on the distributor. 

    1)  One could drill and tap the Webber's intake manifold 
        to accept a second vacumn line (most of the conversion 
        kits I have seen include a round flat spot on the top of
        the manifold for this purpose), but this would force you 
        to remove the manifold to make the modification.

    2)  You might want to experiment with a Tee fitting on the
        existing vacumn line, and connect both the vacumn advance
        AND the anti-run-on valve, since the net pressure should
        roughly equalize regardless of the details of the 
        connections.  Please note that I have no idea of the net
        effect of using an anti-run-on valve with a Webber.

    3)  To my knowledge, the vacumn port on at least the Webber 
        down-draft carbs is a very stange beastie when compared 
        to the usual set-up with dual SUs.  The vacumn is a 
        steady (manifold) pressure with the SUs, but the Webber 
        carb vacumn port provides a "pulsed" vacumn, which tends 
        to frustrate the vacumn advance mechanism.  I do not use 
        the built-in vacumn ports on either of my dual Webber 
        DGVs, I use a vacumn line on the manifold itself.

 www.ill//somebody ple@se expl@:n th:s wwweb @address.bu:s:ness?
 james fischer             

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