On 6/18/96 2:32AM, in message <9606180832.ZM11400@zeu.tt.umist.ac.uk>, "Chris
Boston" <spitfire@zeu.tt.umist.ac.uk> wrote:
> 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.
> --
>
Dave,
I have a 1970 MK III Spit with HS2's. I agree with everything that Chris
pointed out except that my engine runs best at 8 BTDC dynamic. The other thing
I would recommend is to get the rebuild kit and rebuild the carbs. The kit
does not cost much and it forces you to CLEAN and reset everything. I had a
lot of trouble tuning my carbs untill I did the rebuild. Now my carbs are easy
to tune (or as easy as they can be) and the tune dosen't seem to change much.
The other important item is a good shop manual. The book titled "SU Caburetors
- Tuning Tips and Techniques" is a good one to have.
Hope this helps,
Bill Munts
1970 MK III Spitfire
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