[Healeys] Setting SU HD Carburettors

[Derek Job]

Bob

My understanding was that you adjust the  idle with the slow run valve and
not the throttle adjustment. In fact i have read in various publications
the instruction that the butterfly must be closed at idle.

Here is an example from a US company called British Classic Motors.

'On most vehicle applications the idle is controlled by the slow running
running valve and this alone must be used to adjust the idling speed.
IMPORTANT: It is imperitive that the throttle linkage is allowing the
butterflies to close completely. If not, it will not be possible to set the
idle speed accurately'.

Derek

On Fri, Aug 17, 2012 at 6:26 PM, Bob Spidell <bspidell at comcast.net> wrote:

> re: "Does anyone else out there find this contradictary."
>
> Not after you've read the instructions about 37 times. (I think) it means
> that in Items# 2&3 disregard the instructions--probably written originally
> for single-carb applications--and use the throttle adjusting screws instead
> of the slow-run valves.
>
> My technique is to set a slightly slow idle with balanced airflow with the
> throttle adjusting screws with the slow-run valves closed, then open up the
> slow-runs equally to get the desired idle speed (and rebalance).  This way,
> when I'm at high(er) altitude--my base tuning is near sea-level--I can open
> up the slow runs an equal amount; e.g. a half-turn, to bring the idle back
> up, then turn them back down when I get back down to SL.
>
> Also, I prefer for the 'throttle stops' to, well, stop the throttle plate
> than have it slam against the bore.
>
> Bob
>
> --------------------------------
> Bob Spidell - San Jose, CA
>
> ------------------------------
> **
> I just obtained a copy of the SU Workshop Manual.
>
> Flicking through the HD section I noticed the following
>
> 1. On single carb applications the idling speed is adjusted by using the
> slow running valve.
>
> 2. On Multi carb applications  there is the following statement.
>
> Item 1
> Note: *Whenever the throttle adjusting screws are fitted they, and not the
> slow running valves, must be used to adjust the idling speed*. Screw down
>
> the slow-running valves (which must remain closed) and set the throttle
> adjusting screws 1.5 turns open. In items 2 and 3 adjust the idling speed
> with the throttle adjusting screws.
>
> Item 2 says:
>
> a) restart the engine and turn the slow-running valve *OR* the throttle
>
> adjusting screw, an equal amount on each carburettor to give the desired
> idling speed.
>
> Item 3 says:
>
> a) Turn the jet adjusting screw an equal amount on all carburettors, up to
> weaken or down to enrich, until the fastest idling speed consistant with
> even running is obtained
>
> b) Re-adjust the slow running valves, if necessary.
>
> Does anyone else out there find this contradictary. Are the slow running
> valves to be used to adjust idling or not?
>
> Any thoughts?
>
> Derek