Fuel System: 140 Carb: SU HIF6 Carb inlet adjustment?!@#

[MyStylesTheBomb]

Howdy all. I have a '70 144S (USA) with SU HIF6 twin carbs. It seems there are two mixture adjustments on this carb instead of the usual single jet raise/lower nut on plain ole' SUs. It's right where the fuel goes into the carb - there is an adjustment nut there sorta like the idle adjustment screw. Then the main jet adjustment seems to be to the bottom right of the air inlet throat, at an angle. I've looked at several pdfs I found on line and none of them address the fuel inlet adjustment.

Could it be the float level?

Could anyone please a) enlighten me on the fuel inlet adjustment and how it should be used and b) bonus question confirm the angled screw below and right of the air inlet throat (front carb) is the main jet adjustment?

Thanks, Scott (photo attached)

p.s. They are parts 40,41, and 42 here on page 67, just noted as lever, screw, and nut: http://global.gcp.se/global/catalogues/nav47272?type=sc

[Volvorama]

Great carbs. I use these to convert Stromberg cars. The one I use is the same as the later USA spec 144s but I usually get them as a carb for a British Austin car and change the needle.
Firstly, the SU only has one jet and this is adjusted by the slot-head screw that goes in at an angle towards the base of the carb. It operates a lever that pushes the jet up and down.
Secondly, the other slot-head screw goes in from above and is just a throttle stop screw to adjust the tickover speed.
So far I've just done single HIF conversions but I bought a pair of Volvo HIFs on ebay from California but have not used them yet. In the UK and Europe we didn't get the SU HIF as instead they switched to twin Strombergs - horrible!

Added: On those excellent parts diagrams I believe that the fuel mixture adjuster is the screw no. 16. Tickover adjustment is No. 31. The parts 40, 41 and 42 are something to do with a ventilation system (air injection into the exhaust for emission control?) and are operated BY the carb and do not affect the tickover. My USA carbs have them too but they won't be needed. The little slothead screw in your photo is 2a I believe and this is just a plug. It does nothing but needs to be there.

[Volvorama]

I now realise that the the 'ventilators' are probably to do with the US spec stuff that takes away petrol vapour from the carbs. There's a little metal tank in the boot where it condenses and is returned to the tank. The mechanism on the side of carbs is, I believe, operated by the throttle so that it only vents when the engine is ticking over.
I have an American '69/70 144S and it has this system but it was disconnected long ago.