Slow running screw

[Azzura]

In the SU Manual it says " that wherever throttle adjusting screws are fitted they, and not the slow running valves must be used to adjust the idle speed.

Does that mean the slow running valves are screwed down and left closed?

Setting the idle is then just on the throttle adjusting screws alone.

[piman]

Hello Azzura,

something doesn't sound right? I presume a HD carburettor, which is the only one I know of with a slow running screw.
Basic setting is 3.5 turns up from fully closed and then it is used to set the idle speed when the engine is running at normal temperature. The other speed adjusting screw is the fast idle operated when the choke is on.

Alec

[Azzura]

Hi Alec,

Thanks for taking time to respond, much appreciated

This is a standard E Type 4.2 set up with triple SU's (1969 Series 2) 18 months of restoration later!

So far I have been setting it up with the slow running valves ( the chunky ones) completely shut. So adjusting the tick over on the throttle adjusting screws. This is from the SU manual supplied by Burlen. The engine goes well and ticks over quite happily. It was only after changing air filters and other stuff that I noticed one part of the manual says:

"That wherever throttle adjusting screws are fitted they, and not the slow running valves must be used to adjust the idle speed."

So I left the slow running valves, as they call them, screwed down.

Then further on in the manual (part 4) it says "Re adjust the slow running valve if necessary to give correct idling."

A bit conflicting it seems, but perhaps you adjust one before the other, simple as that?

Cheers

Roger

[piman]

Hello Roger,

it was a Burlen manual I got the initial screw setting.
I had a car with similar triple 2" HD8 carburettors but don't remember any throtlle adjusting screw apart from the fast idle.

Just had a look in the Burlen manual again and I see the section you refer to.It does say to shut the slow running jets. I can only assume that this set up is a manufacturers favoured installation rather than S.U.s. There seems little sense in adding throttle adjustment for slow running when that is already built into the carburettor. Possibly they had problems and decided to use throttle linkage adjustment for reliability for instance?

Anyway, yes it seems they should be screwed shut.

Alec

[Azzura]

Thanks Alec,

I will leave it be!

Cheers for now

Roger