I've been working on my Weber book and want to share a bit of tuning information that may be of interest.

Off-idle optimization

The optimization of this region of operation may be quite tedious as it requires removal of the Webers for inspection of the alignment of the throttle valves with respect to the first progression holes in the throttle bores. This process is important to ensure the throttle valves immediately begin to expose the first progression holes with the slightest throttle opening to assure sufficient fuel is added to provide mixture strength with the increased airflow.

An additional reason to check for this alignment is to assure no supplemental fuel is added to the idling mixture. Since fuel for the idle and progression circuit is the summation of fuel delivered via the mixture screw and the progression holes, partially exposed progression holes will result in a decreased fuel delivery from the idle mixture screw thereby decreasing total fuel delivery during progression and transition.

NOTES:
• IDA, IDA(S), IDS, IDAP and IDT Webers routinely have the throttle valves close below the first progression hole at idle.
• IDTP and IDTP1 Webers are particularly susceptible for exposing the first progression hole at idle.
• Worn Webers tend to leak air past the edges of the throttle valves resulting in a more closed idling position. This causes the edges of the throttle valves to be somewhat below the first progression holes which results in a lean stumble off idle.

The procedure for optimizing the alignment of the throttle valves with the first progression holes is:
• Perform Lean Best idle mixture adjustment including idle air flow balancing
• Remove the carburetors from the intake manifolds and observe throttle valve position with the first progression hole. If the edges of the throttle valves are all below the first progression hole then you may file the lower edge of the throttle valve until it just coincides with the bottom edge of the first progression hole. File the edge keeping the file alignment as parallel as possible to the plane the valve is in.
Note: This adjustment will not affect Lean Best tuning as performed prior to carburetor removal.
• If the throttle valves are partially exposing the first progression holes, then the following procedure is to be executed:
o Adjust the throttle stop screw to allow the throttle plates to close against the throttle bores
o Open the throttles using the throttle stop screws until the first progression holes are just beginning to become exposed by the edges of the throttle plates.
o Count the number of revolutions the throttle speed stop screws are turned to achieve this condition and record the information for use during periodic tuning.
o Some valves may be retarded in this adjustment compared to the others. If that is observed, then use a small file to relieve the bottom side of the valve until the bottom edge matches the alignment of the valves that just block the first progression hole. File the edge keeping the file alignment as parallel as possible to the plane the valve is in.
• Reinstall Webers, start engine and perform air flow balancing using ONLY the idle air correction screws followed by Lean Best idle mixture adjustment. DO NOT adjust throttle stop screws. Adjustment of throttle stop screws will upset the throttle valve alignment with the first progression holes.

NOTE: If the above procedure results in the idle air correction screws to be opened to their maximum adjustment position, then remove the Webers and drill a 1.5mm diameter hole in the throttle valve, in the center of the valve, close to the throttle shaft. Close all idle air correction screws and repeat the air flow balancing and Lean Best adjustment as before.