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Re: Problems tunning dual SU HS2's on Spitfire

To: Dave Chu <dave@ECE.concordia.CA>, triumphs@autox.team.net
Subject: Re: Problems tunning dual SU HS2's on Spitfire
From: "Chris Boston" <spitfire@zeu.tt.umist.ac.uk>
Date: Tue, 18 Jun 1996 08:32:10 +0100 "Problems tunning dual SU HS2's on Spitfire" (Jun 17, 2:10am)
References: <9606170612.aa27069@ece.ECE.concordia.CA>
Dave,

I'm not sure about the HS2s, but I retuned my HS4s last night.

BEFORE TOUCHING THE CARBS: Make sure everything else is set first, eg tappets,
points, timing, plugs, etc.  THEN:

1. disconnect the choke cable.

2. Screw the fast idle screws well clear of the cams.

3. Clean Everything!

4. Screw the jets up to be flush with the bridge. (mark the fronts for ref.)

5. Screw the jets down by twelve flats (2 complete turns)

6. Start the engine and get the car up to temperature if not already.

7. Balance the carbs and set the slow idle speed, using a balance meter.

8. Run the engine at 2500 revs for at least 30 seconds.

9. Check the emmissions, or use a colourtune to check mixture.

10. Adjust both jets equally, up to weaken, down to enrich.

11. When correct, re-adjust and balance the slow idle if necessary.

12. Connect the choke cable, leaving about 1/16 inch free play.

13. engage the choke to the point where it is just about to enrich the jets.

14. Set and balance the fast idle using the balance meter.

NOTES:
------
If correct mixture setting cannot be achieved within a couple of minutes, run
at 2500 rpm for thirty seconds again before continuing.

Adjust jets by one flat at a time (same direction on both carbs), allowing a
little time for the exhaust meter to catch up (or colourtune to stabilise).

If the jets need adjusting by more than about 4 flats, there is likely to be a
problem with one or more of the carbs.

Slow idle speed 650 to 850 rpm

Fast idle speed 1100 to 1300 rpm

Emmissions (UK HS4) 2.5 to 4.5 percent

Dwell angle 46 to 56 degrees

timing (UK 1500 spit) 10 degrees before top dead centre

valve clearences 10 thou. when cold.

spark plug gaps 25 thou.

*** ABOVE ALL***, Make sure that everything else is set correctly before
touching the carbs.

I hope the above is useful, but I must stress the above fugures and procedures
applies to the HS4s on my UK 1500.  I cannot vouch for their applicability to
HS2s on a US spec car.

Good Luck,

Chris.

-- 
-- 1977 Spitfire 1500...Everyday/Only Driver.
--

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