I have a set of 40mm Dells on my car which are running well but I am trying to get my head around some theoretical issues.
Carby feeding No's 1 & 2 cylinder mixture screws are between 1 and 2 turns out.
Carby feeding No's 3 & 4 cylinder mixture screws are between 3 and 4 1/2 turns.
Also 1 & 2 carbs idle speed screw is 2 to 3mm further out than 3 & 4 carb but butterflies are open the same amount(3 thou).

Why would this be so?

Carbs have been synced with a uni-syn and all 4 barrels are the same.
I have been pondering over this for a week or so and can't seem to figure it out. Any ideas? cheers Adam

I run a set of 48mm DRLA's on my ghia, have you checked the idle jet sizes with a jet gauge, if they have the same size stamped on all four it does not mean they have not been drilled out, this is what i would do with all the jets so you know you have all the same sizes . then you have a known starting point.

Agree with the above.
Have you also had the idle mixture screws out to check they are in good condition?

Or the idle mixture screw O-rings? Or any of the seals and O-rings for that matter

Thanks guys, do you know what size O rings the idle mixture screw takes as I would be able to get some from work. Jets are definitely the same size. cheers

My guess is around 4 x 1.5 but that is purely by memory