All of our Webers are identical in performance potential once the main circuit is activated. The IDTP carburetors have a progression circuit design that is mated to suit smaller main venturis (27mm to 30mm) and all other progression circuits used in the various type permutations for our cars are similar and more appropriate for larger main venturi sizes.
When I say "performance potential" I mean you may install main jets, emulsion tubes, air correction jets and main venturis and with each item you have the responsibility to decide if that component works harmoniously with the other bits in your Webers and with your particular engine and driving style/application.
If your engine was modified with S-cams and other "upgrades" and your Webers are as they were as OEM for a 911T then you have work to do. However it is difficult to map a course of action without knowing where you are now. The particulars of your Webers may not be important if you do not care for cost impact of component changing but if you do want to control costs then it would be best to list what is currently installed in your Webers.
Those items of interest in your Webers are:
- main venturi size
- idle jet size
- main jet size
- emulsion tube type
- main air corrector size
- part number of your Weber (IDA, IDS, IDT, IDTP or IDAP)
Since your issue occurs well within the range of main circuit operation the details of the idle/progression circuit are moot. Emulsion tube type may be the culprit since WOT is mostly the interaction of the main jet size and the main air correction jet size. When you are at partial throttle the emulsion tube has more contribution to fuel mixture than when at WOT.
I believe the OEM emulsion tube for your Webers is a F1 which has a rather large outside diameter that extends for much of the length of the tube. This large/long diameter "fills" the emulsion tube well with metal that restricts the flow of gas past and also excludes gas from the well. Since partial throttle opening acceleration performance is the domain of the emulsion tube it stands to reason that your emulsion tubes are hindering fuel delivery. Typical emulsion tube selection for "S" specification pistons/cylinders is F3 but that assumes IDS carburetors with the high speed enrichment tubes. F26 emulsion tubes are also a good choice but require larger main jets and smaller air correction jets to work than when F3s are selected.
Of course, your distributor is worthy of inspection as well but I believe most of the dizzys are at full advance at your RPM range so for there to be an advance issue that occurs within the 3000 to 7000 RPM range but does not cause trouble at 3000 RPM or at 7000 RPM would be difficult to imagine. Someone provide more sage input here, please.