[Healeys] Setting SU HD Carburetors

[Derek Job]

Dave

I think thats right about the Aston Martins. It was mentioned in the
article I read.

When you re-read the workshop manual with the knowledge that not all HD8s
have throttle adjusting screws then the wording does make sense.

Derek

On Fri, Aug 17, 2012 at 7:24 PM, David Porter <frogeye at porterscustom.com>wrote:

> I could be wrong but I think the only HD8's without a slow run adjuster
> (AKA
> air bleed) are fitting to Aston Martin's or perhaps the odd purpose built
> race engine.. The double mechanical only is one to keep the butterfly valve
> from sticking-the other for idle adjustment.
> dave
>
> frogeye at porterscustom.com
>
> Porter Customs   2909 Arno NE
> Albuquerque, NM USA 87107
> 505-352-1378
> 1954 BN2  1959 AN5
> Porter Custom Bicycles
>
> cars:
>  www.britishcarforum.com/portercustoms.html
> gallery:
> http://picasaweb.google.com/porterscustombicycles/PorterCustomBicyclesStuff
>
> GO HERE: http://porterbikes.com/  nice pictures-fun facts-my world
>
>
> 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
>
>
>
> 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?
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