[Healeys] Setting SU HD Carburettors

[warthodson at aol.com]

Yes, I have observed the apparent contradictions. Many of the available
instructions are confusing & use inconsistent terms for the various adjustment
components on SU's. I contacted Burlen Fuel Systems concerning why single
carbs & multi carbs would require different adjustment procedures. They
replied that they were to busy to answer my question.
I did find a partial clarification in their own literature.  Burlen
publication No. 1495 dated 1988 describes the adjustment sequence just like
you described, however note that it says "whenever the throttle adjusting
screw are fitted". As clearly shown in this publication the throttle adjusting
screw is not the same as the "fast ldle adjusting screw". These two adjusting
screws are located close to each other & are often mistaken for one in the
same. As far as I can tell, none of the HD's fitted to Healeys came fitted
with the throttle adjusting screws. That would explain why none of the Healey
work shop manuals ever mention adjusting the idle with anything but the
"slow-running valve".
However, there is a "Catch 22". I have had no trouble adjusting the ilde using
the slow running valve on double or triple HD4 or HD6 carbs on Healeys, but I
have had frequent trouble adjusting the idle with the slow running valve on
HD8's. The HD8's, more often than not, do not seem the respond to the slow
running valve. I have been told it is because the o-ring around the slow
running valve is old & worn, but replacing it has never made any difference
for me. This is the reason so many people resort to adjusting the idle on
HD8's with the fast ilde adjusting screw, but they mistakenly think they are
using the throttle adjusting screw which is not fitted the Healey HD's.
Is that clear?
Gary Hodson