[TR] SU Carbs

[G.D. Huggins]

Roger,

I just spent last week adjusting my carbs; exploring the relationships between
timing, idle and mixture.
I have HS6's, but those are similar to the HS4s.

I basically had the same issue as you with the throttle screws barely touching
the plates, and the engine idling higher than it ought.
So I got the mixture set, which had a small impact on the idle, but not much,
with it still idling around 1000 rpm.
So, I retarded the timing a bit to tame the idle, but not too much to cause a
loss of power, overheating, etc.

I learned that you can retard the timing too much, and the car just will not
respond to throttle under load.
The exhaust gasses can also get very hot (because they are not burning up all
the way in the cylinder) and overheat the exhaust system.

The point is to find the correct tuning balance between timing, idle and
mixture.



On Apr 24, 2012, at 8:43 PM, Roger Elliott wrote:

> Hi,
>
> I am trying to adjust the dual HS4s on my 80 Spitfire.  I adjusted the carbs
to the recommended starting point to try to get a fresh run at adjusting
them.
>
> Turned the jets down 12 flats (2 turns) and then turned the throttle screw
down 1 1/2 turns after it just came into contact with the lever.   I noticed
that the  throttle screws were not in contact with the lever when I started.
>
> When I started the car it was running about 2600 rpm.  When I got it back
down to close to 1,000 rpm, it looks like the throttle screws were no longer
touching the levers.  Choke seems to be off, the fast idle screws are not
touching. I rebuilt the carbs about 4 years ago.
>
> I did not take them off, but it looks like the butterfly is closing well.
>
> Any suggestions on what to look at, before I take the carbs off to inspect
the butterfly more closely?
>
> I have adjusted the valves, and timing.
>
> Thanks,
> Roger Elliott
>
> ** triumphs at autox.team.net **
>
> Donate: http://www.team.net/donate.html
> Archive: http://www.team.net/archive
> Forums: http://www.team.net/forums
> Unsubscribe/Manage:
http://autox.team.net/mailman/options/triumphs/guy@genfiniti.com