At idle, the little levers (on the linkage) that fit between the forks
and move them should NOT be touching the forks1 The idle
adjustment screws act directly on the forks, NOT on the linkage.
As you open the throttle from idle, the levers should first move a little
bit before touching the forks and starting to move them off the idle
position.
Doug Braun
'72 Spit
At 11:24 AM 5/2/00 +0100, Dean Dashwood wrote:
>Tim,
>
>Did you manage to fix this?
>
>I finally got round to looking at the problem on my car this weekend, and this
>is what I found. (Apologies if I use some incorrect terminology, I don't
>really
>know my way around carbs.)
>
>Attached to the throttle disk (is that what it's called?) on each carb is a
>fork, which is acted on by the throttle linkage when you apply pressure to the
>pedal. When pedal pressure is released, this fork is moved back into position
>by a spring (one for each carb) attached to a tab bolted onto the inlet
>manifold, until it reaches the idle-screw (or part of the choke mechanism,
>although I was working with the engine hot and the choke in, so this
>didn't come
>into play). The linkage plays no part in returning these forks to their
>"home"
>position. The forks/disks on each of the two carbs move completely
>independantly of each other.
>
>I played with the accelerator until the engine was revving a little high, then
>took a look at the carbs, and found that the forks on both carbs had not quite
>moved back all the way to the idle-screws. The engine was idling at around
>1500rpm. Using my fingers, I could push the fork back about another 1/32
>inch,
>or maybe even less, on one carb, and the idle dropped to 1200rpm. Repeat
>on the
>other carb, and the idle drops to a perfect 900rpm.
>
>I cleaned the entire area using a liberal amount of carb cleaner, and also
>bent
>back the tabs the springs attach to on the manifold to get a bit more
>tension in
>the springs, but this didn't help.
>
>I'm now open to suggestions from the list as to what to do
>next. Hopefully this
>will help Tim fix his almost identical problem, too.
>
>Cheers,
>
>Dean
>'77 Spit 1500 with twin HS4s
>-----------
>
>
>
>
>
>Date: Mon, 17 Apr 2000 08:30:07 -0400
>From: "Dean Dashwood"
>Subject: RE: Throttle control problems
>
>
>Tim,
>
>I have an identical problem to this. I also have twin SUs (HS4s) and
>until this
>weekend the car would often idle at around 1500rpm, with a little blip on the
>throttle settling it back down to 750rpm. This didn't bother me (1500rpm
>is not
>too much to handle) but I put it down to the frayed throttle
>cable. Eventually
>got round to replacing the cable, but this made no difference, so I forgot
>about
>it.
>
>Since getting a little too close to the tyre-wall this weekend, though,
>the idle
>speed has gone up to about 2500rpm, with a blip on the throttle usually
>putting
>it back to normal, but sometimes making it worse, so I was planning on looking
>at it in more detail this weekend. My first plan was to check the pistons in
>the carbs.
>
>If you fix this, I'd be interested to know what it was. Likewise, I'll
>let you
>know if I manage to fix mine.
>
>Dean
>---------------
>
>
>
>
>Date: Mon, 17 Apr 2000 08:30:07 -0400
>From: "Bowen, Patrick A RP2" <PABowen@sar.med.navy.mil>
>Subject: RE: Throttle control problems
>
>Tim, my answer would be you have a frayed cable, but you say it is new. I
>would take a second look at it anyhow.
>
>Patrick Bowen
>
>- -----Original Message-----
>From: T. .R. Dafforn [mailto:td214@cam.ac.uk]
>Sent: Monday, April 17, 2000 5:44 AM
>To: spitfires
>Subject: Throttle control problems
>
>
>
>Hi Listers,
>Finally after 2 1/2 years my car is legal again...
>However I have just picked up a problem...
>While driving back from the test station the throttle seems to stick
>open causing the car to idle at 3K rpm...
>Quick blip on the throttle and it dropped back to idle at 750 rpm...
>Then it happened again 5K rpm...
>blip and back down..
>Got back and had a look at the throttle linkages, they seem fine
>although the car has never had the return spring which attaches to the
>header are these required? It has always relied on the return springs on
>the carb...
>Also noticed that the rear float bowl was leaking where the tube from
>the jet screws in....
>Does any one have any ideas whether the problem is mixture or sticking
>throttle cable (which btw is brand new!!)
>hope some one can help
>cheers
>Tim
>PS the car is a 1500 twin SU carb...
>
>- --
>Tim Dafforn
>Structural Medicine
>Department of Haematology
>CIMR
>University of Cambridge
>Wellcome-MRC Building (Level6)
>Hills Road
>Cambridge
>CB2 2XY
>
>Tel. (01223) 336829
>Fax. (01223) 336827
>http://smokeroom.cimr.cam.ac.uk/
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