[Healeys] Setting SU HD Carburettors

[Derek Job]

Gary

Yes i have four adjusting screws. One chap I was talking to assumed the
throttle screws had been added later by a PO because the slow running valve
wasn't working properly. This is the first car I've had with HD8s. The car
was built up to fast road spec, it has a BJ8 engine installed in a 100-SIX
but I have no idea where the carbs came from.

Derek

On Fri, Aug 17, 2012 at 7:04 PM, <warthodson at aol.com> wrote:

> 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