Hi,

I’m a 240 man and I’m chatting due to the BRICKBOARD being so dead in my section.

I grew up in the age of sixties motorcycles before the days of water cooled engines.
Graduation to owning a new 1974 pickup truck still meant a junkie carburetor.
The same year of the gasoline embargo and $.64 a gallon gas. Up from $.24 a gallon.
Then I bought 1978 Volvo with a Bosch K Jet 2.1 L.
What a welcome change for me! 29 MPG highway, not 12 or 13 on a tail wind day.

What I know of carburetors the adjustment screw adjusts the gasoline amount to the amount of air passing through the throats of the units. They may call it “air bleed” but carburetors handle gasoline.
Think of it as tall bucket with various holes in the bottom half that bleed gasoline.
Jets and screws are used to vary the hole sizes.

I say throats because the term barrels is used to count either the number of carburetors or the type of carburetors.
As a kid I hung out with dirt oval track racers. They ran eight one barrels on their engines.
A rack of red rubber balls were popped into the Venturis’ and tapered hickory blocks into the exhaust pipes upon shutting down the engine to stop valves from being warped. Straight pipes throwing noise and flames!
Entertainment for the Southerners, like fireworks? (:-)

So, with that long breath, I say treat the idle mixture screw is like a water faucet. The more it moves away from the seated position the more fuel you will get and therefore a richer mixture.

Just a side note on small engines with a carb the starting out standard is 1&1/2 turns out.

The setting of the throttle plate being “cracked open” is for the curb idle speed.
The cracked opening is what pulls the fuel out into the air stream.
The two work back in forth with each other and so this is where the term “tuning” comes into play.

On motorcycles of the late sixties, especially Hondas, manometers were use to synchronize the evenness of air amounts.
With the six cylinders Hondas this was very important for even heating of an air cooled block.
The center cylinders were the ones needing a slightly different treatment the the outer cylinders.
The advent of racing jetting with volumetric sensitive KEIHIN carbs came on the scene.
This is where diaphragms appeared on top of throttle slides.

I know nothing about Strombergs or SU’s other than the names I have read of.
They could be the same for all I know?(:-)

Long answer for a short question but hey, I bored! But not enough to want carburetors again.

Carburetors can do a wonderful job though, as everything is about finding a compromise and carburetors kept it simple, to some very real extent, for a very long time!
Maybe too long?
Without computerization Internal combustion should have stopped.
With the future embarkation into electric vehicles, it is going to be anyones guess, to how far the next century will takes us to being more simplistic, again?

Phil