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Tuning Dual SUs

To: tr8@mercury.lcs.mit.edu (TR-8 mailing list),
Subject: Tuning Dual SUs
From: gavin@csis.dit.csiro.au (Gavin Walker)
Date: Mon, 13 Jun 1994 16:47:10 +1000 (EST)
Hello Guys
  Well after 7 weeks I've finally finally fired up the Rover SD1 with
Dual SU HIF 6s (was Stromberg).  There was a mighty roar, great
belches of smoke and lots of panic as I tried to keep the car going
and finish filling the cooling system at the same time.

  With the cooling system stabilised I proceeded to tune the carbs.  I
have Roger's tuning sheet but I decided to use the tools at hand
instead.  I have Gunson's Car Balancer and Colortune.  Here are the
steps I went through

Balancing the carbs
  1.  Disconnect the left carb from the accelerator cable lever.
  2.  Loosen the throttle loss screw so both carbs work on their own
  idle speed screws.
  3.  Using the car balancer I adjusted each idle speed screw to give
  the same reading and have the revs about 800 rpm.

  My right hand carb wouldn't give a steady reading.   It'd be steady
for a few seconds then drop down and soar up for a few seconds then
drop again.  I tried to use the position it stayed at the most as it's 
mark.  When I was sort of happy I reconnected the accelerator and set
the throttle loss screw.

Setting the mixture
  1. Put the colortune in and start the engine.
  2. Turn the idle mixture screw until a yellow flame appears.
  3. Back it off until the yellow flame disappears.

I used the 4 cylinders on the right bank, two are fed by each carb.
On ones fed by the right hand carb I had trouble getting rid of the
yellow.  The flame would occasionally have spurts of yellow.  I did
the best I could.  The engine still isn't all that smooth.  I expect 
it to be smoother than my 4 banger.  

When I got to turning it the car had don't about an hour worth of
idling.  All spark plug were installed new and ones from the right
carb were covered in soot, while ones from the left carb looked (if a
bit rich).  In getting the car started I had turned the right carb
idle mixture screw an extra full turn.  These carbs had been rebuilt
from scratch a couple of months ago and the default setup of the idle
mixture screws was bring the jet level with the bridge and up (or was
it down) two turns.

When I get the wheels back on I'm considering going through Roger's 
method (The car will be easier to warm up then).  Does anyone have 
any tips in this process?  I don't want to take it to a pro just yet.

-- 
  _--_|\             -|-    Gavin Walker
 /      \             |     
 \_.--.*/ <- Canberra,      gavin@csis.dit.csiro.au
       v     Australia      Phone +61-6-2750964     Fax +61-6-2576325


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