Here is a link which has much information about the W-1 carburetors:

http://www.thecarburetorshop.com/CarterChevroletW1.htm

Here is a link that has information about adjustmenets:

http://www.thecarburetorshop.com/Dual1barrelcarbs.htm

The "long needles" are the metering rods. The best approach is to build the W-1's to absolute stock condition; and then adjust from there. Depending on what has been done to the engine (compression, cam, headers, etc.) very little may be needed to modify the carburetors.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop