[Healeys] Setting SU HD Carburettors

[warthodson at aol.com]

I don't know for sure why the throttle adjusting screws would be fitted. One
theory is that the slow run screw becomes less effective when multiple cars
are fitted because the air velocity is so low at idle with multi carbs.
Another theory is that the butterflies are difficult to perfectly center in
the carb bodies & therefore some air is always leaking thru, even when they
are closed & this adversely affects the idle circuit operation.
If your HD's have have throttle adjusting screws then you should be able to
identify four separate adjusting screws/carb as follows: Slow-running valve,
fast-idle adjusting screw, jet adjusting screw, throttle adjusting screw. Do
you have all four?
Gary Hodson

-----Original Message-----
From: Derek Job <derek.c.job at gmail.com>
To: Bob Spidell <bspidell at comcast.net>
Cc: Forum <Healeys at autox.team.net>
Sent: Fri, Aug 17, 2012 12:47 pm
Subject: Re: [Healeys] Setting SU HD Carburettors


Gary that is a very interesting comment you make about the throttle
adjusting screws not being confused with the fast idle screws.

I seem to have a pair of HD8s on my car which do have throttle adjusting
screws as well as fast idle screws. The slow running valves were screwed
down and the adjustment has been made on the throttle screws. I still don't
fully understand this though. For instance, what is the purpose of the
throttle screws if the carbs operate fine without them. What extra benefit
do they offer. Any ideas?

Derek