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fast idle screw on SU H4 carb

To: british-cars@hoosier
Subject: fast idle screw on SU H4 carb
From: Croaker the Physician <markl@us.oracle.com>
Date: Tue, 8 Sep 92 17:16:29 PDT
A question about the fast idle on my MGA's carbs.  There is a single screw
which does the very obvious thing: turn the screw down and it pushes a small
plate which opens the throttle.  Turn the screw up and the throttle closes
until it hits the normal idle stop.

Alas, my screw appears to be screwed.  So to speak.  I cannot get it screwed
down enough to make any meaningful difference in the idle, due to a tension
spring in between the screw head and the plate into which the screw threads.
The result is that when I use the choke, I get a nice rich fuel mixture, but
no fast idle, and the car runs very roughly (richly) until it is warm enough
that I can start backing off the choke.  If I do the old manual fast idle
(foot on the accelerator :-), the engine smooths out nicely, but I get tired
of doing that.  If I back off the choke completely, the car sputters because
it is cold.

So the question: what's the problem with the screw, and what should the fast
idle setting be anyway?  I suspect the wrong screw is in there and is too
short or something, but I want to be more sure before I go and mess with it.

Thanks for any assistance,
markl

----------
Mark L. Lambert
Architecture Group, Network Products Division
Oracle Corporation

           Internet: markl@us.oracle.com
           UUCP:     ...uunet!oracle!markl
           USMail:   Oracle Corporation
                     Box 659410
                     Redwood Shores, CA 94065

"The parts falling off this car are of the finest British quality..."

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